THE FRESH-WATER FISH AND FISHERIES OF z’AKISTAN WIYH SPECIAL REFERENCE TO FISH CULTURE FGR FOG-D Thesis for II" Degree of DH. D. MICHIGAN STATE UNIVERSE-TY Shamsud Doha 1964 THESIS This is to certify that the thesis entitled The freshawater fish and fisheries of Pakistan with special reference to fish culture for food presented by Shamsud Doha has been accepted towards fulfillment of the requirements for Ph. D degree mFisheries and Wildlife ,r/,7 I i ”7- I, /," MM j W“ Peter I. Tack, Major professor Date February 20, 1964 0-169 ?'J LIBRARY 1 Michigan State g 3 University _.,--.— ls..— W... ‘I if ..\"1I I K.‘ ABSTRACT THE FRESH-WATER FISH AND FISHERIES OF PAKISTAN WITH SPECIAL REFERENCE TO FISH CULTURE FOR FOOD by Shamsud Doha The nature and present condition of the fresh-water fish and fisheries of Pakistan with Special reference to fish culture for food have been investigated. The timeli— ness and importance of such a study cannot be exaggerated in view of the fact that fresh-water fishes supply nearly 40% of the necessary animal protein to balance the rice— vegetable diet of the Pakistanis. The fishery resources of Pakistan have not yet been properly assessed. The fresh-water fisheries constitute nearly 70% of all fisheries of Pakistan. Over 300,000 ponds, four large and numerous small rivers and streams, lakes, swamps and rice fields support the fresh-water fisheries. The productivity of these waters are believed to be quite high, but the traditional practices of fish culture and fish— ing in these waters have not significantly increased the catch. The pond cultural practices (”teichwirtschaft”) in Pakistan (East Pakistan, in particular) are quite extensive. Shamsud Doha As the indigenous carps Spawn in rivers and not in culture ponds, the Pakistani fish farmer must depend on the timely supply of the stocking material. Difficulties in the trans— port of fish fry to the numerous stocking ponds situated far away from the Spawning grounds limit, to a great extent, the maximum utilization of ponds for fish culture. Ponds are not constructed in Pakistan on a Scientific basis. A domestic pond which is excavated for the supply of necessary earth for house building is used for a variety of purposes: it supplies drinking water, it is used for bathing as well as washing, it is also stocked with fish, mainly carps--katla (Catla catla), rohu (Labeo rohita), mrigal (Cirrhina mrigala) and kalbaus (Labeo calbasu). Ponds are never limed or fertilized with standard inorganic fertilizers. Carps and other food fishes which are fattened or raised in ponds depend on the natural fOOd supply of the ponds. Arti- ficial feeding of carps is rarely practiced in Pakistan. From the physico—chemical and biological points of View, Pakistan‘s fisheries in freshéwater rivers, lakes, swamps and rice fields are not well managed. Limnological studies of these fish-bearing waters have not yet been under— taken in Pakistan. Frequently, destructive fishing practices are employed for lack of effective conservation measures. The craft and gear are also outmoded and are not efficient in catching operation. These problems have been studied in Shamsud Doha detail and practical measures for their solution have been suggested. In addition to the problems of fish culture and fish— ing, poor means of preservation, storage, transport and mar- keting have further hindered a greater consumption of the fresh-water food fishes in Pakistan. Chilling and freezing of fish are not practiced in any significant amount due to the high cost involved. Curing (drying, for one) is the usual process of fish preservation in Pakistan. The public health aSpects of the curing process are not adequately stressed. Transport and marketing of fish and fishery prod- ucts are yet to be organized in Pakistan. The socio-economic conditions of the fishermen need great improvement. These problems also have been studied in some detail and practical measures have been suggested to solve them. THE FRESH—WATER FISH AND FISHERIES OF PAKISTAN WITH SPECIAL REFERENCE TO FISH CULTURE FOR FOOD By Shamsud Doha A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Fisheries and Wildlife 1964 To my parents ACKNOWLEDGEMENTS I wish to acknowledge with personal gratitude the suggestions and guidance of Dr. Peter I. Tack, Head of the Department of Fisheries and Wildlife, Michigan State Univer— sity, who Supervised my graduate research and study program. I extend my personal appreciation to Drs. Georg A. Borgstrom and Gerald W. Prescott of the Departmentsof Food Science, and Botany and Plant Pathology reSpectively, who took keen interest in my program and gave generously their valuable time as members of my guidance committee. My Sincere thanks are extended to the United States Educational (Fulbright) Foundation in Pakistan for partial support of this study. I acknowledge with thanks the gen— erous financial support given to me by Drs. Georg A. Borgstrom and Peter I. Tack. Lastly, but not in the least, I am grateful to my good wife, Helen, for her constant encouragement without which this project would have remained incomplete. iii INTRODUCTION Chapter I. A. B. C. II. THE A. B. C. D. E. F. III. TABLE OF CONTENTS THE FRESH—WATER FISH The Habitat l. Rivers and Their Expansions Taxonomy and Distribution Respiration of Fresh-water Fishes FRESH—WATER FISHERIES Production Fishing Craft and Gear 1. Craft 2. Gear Preservation Transport and Marketing Consumption Nutritive Value FISH CULTURE A. B. General Historical Basic Ecological Principles The Ecosystem The Food Chain DWNI-i Introduction of Exotic Species iv Selection of Cultivable Species Page 16 20 20 25 25 28 36 50 58 59 65 65 67 69 69 71 72 75 Chapter III. Page Continued. 5. Raising Euryhaline Fish in Fresh- waters . . . . . . . . . . . . . . . 77 D. Cultivated Species . . . . . . . . . . . 78 1. Breeding Habits and Requirements . . 84 2. Possibilities of Artificial Propagation . . . . . . . . . . . . 89 E. Procurement of Stocking Materials . . . 94 1. Collection and Hatching of Carp Eggs in East Pakistan . . . . . . . 94 2. Collection of Carp Spawn . . . 97 3. Breeding the Major Carps in Bundhs . 98 4. Identification of Fry . . . . . . . 100 F. Transport of Fish Fry . . . . . . . . . 100 1. Existing Methods and Their Improvements . . . . . . . . 100 2. Physiological Requirements . . . . . 10C 3. Conditioning . . . . . . . . . . . . 109 G. Nursing and Rearing Carp Spawn . . . . . 109 1. Principles . . . . . . . . . . . . . 109 2. Procedures . . . . . . . . . . . . . 111 H. Fish Culture in Fresh—water Ponds . . . 113 l. The Pond . . . . . . . . . . . . . . 114 a. Definition . . . . 114 b. Fish Ponds of East PakiStan . . 115 c. Improvement of Existing Ponds . 117 d. Construction of Fish Ponds . . . 118 2. The Water . . . . 123 a. Physical Properties .of Pond Water . . . . 124 b. Chemical PrOperties of Pond Water . . . . . . . . . . . . . 127 3. The Soil . . . . . . . . . . . . 138 a. Pond BottOm . . . . . . . 138 b. Drying the Pond Bottom . . . . . 140 4. Aquatic Organisms and Their Management . . . . . . . . . . . . . 141 a. Phytobiota . . , , , . , 142 b. Control of PhytObiota. . . . . . 146 Chapter III. Continued. c. Zoobiota . . . . d. Control of Predaceous Fishes Preparation of Pond for Stocking a. Preliminary Steps b. Liming c. Fertilization Stocking Metabolism and GrOwth a. Food and Feeding b. Growth . Parasites and DiseaSeS . Ecology of Fish Parasites Deficiency Diseases Environmental Diseases Fungal Diseases Bacterial Diseases External Parasites Internal Parasites apture and Marketing Capture Marketing USDOO‘QI'hWD-OO‘QD 1. Fish Culture in Lakes, Reservoirs, Swamps and Irrigation Canals MwaH Lakes and Reservoirs Swamps Irrigation Canals Stocking Fishing and Marketing J. Fish Culture in Rice Fields O‘Ut-bWNI—i Water and Soil Conditions Biota . Preparing the Field Stocking . Management Economic ASpectS K. Fish Culture in Brackish-water Swamps and Rice Fields wal-‘I Reclamation of Saline Swamps Fish Culture During Reclamation Ecology of a Typical Bheri Capture . . . . . vi Page 149 150 152 152 153 157 161 166 166 169 172 174 175 175 176 177 178 181 182 182 183 183 183 185 186 186 188 188 190 191 191 192 194 194 197 198 199 201 201 Chapter Page III. Continued 5. Fish Culture After Reclamation . . . 203 6. Economic Considerations . . . . . . 205 IV. CONCLUDING REMARKS . . . . . . . . . . . . . 206 REFERENCES CITED . . . . . . . . . . . . . . . . . . 208 APPENDIX . . . . . . . . . . . . . . . . . . . . . . 230 vii Table 10. 11. 12. 13. 14. 15. LIST OF TABLES Fish in Pakistanis' diet Pakistan's dependence on fish protein Climatological data of Dacca and Lahore, Pakistan, 1900-1960 average Estimated area of cultivable inland waters of Pakistan Air-breathing fishes and their blood circulation . . . . . . . . . Catch of fresh—water fish in Pakistan Catch of hilsa in Pakistan Fresh-water fish production in principal countries, 1958-1960 Fresh-water fishing craft of Pakistan since 1953 Types of fishing gear of East Pakistan Ice production and cold—storage facilities in Pakistan Comparison of essential amino acid content of fish with some foodstuffs Classified list of cultivated Species of fish in East Pakistan Comparative fecundity of some major carps Salient characters of fry and fingerlings of major carps viii Page 12 18 21 22 26 27 29 45 61 79 86 101 Table Page 16. Number of Chinese carp fry that can be tranSported in a container of 18.5 liter capacity containing 8.5 liters of free oxygen . . . . . . . . . . . . . . . . . . 107 17. Distribution of ponds in East Pakistan . . 116 18. Temperature and dissolved oxygen relationship in pond water . . . . . . . . 128 19. Alkalinity and pond cultural Significance . 134 20. pH of soil and approximate quantity of C30 required to neutralize it . . . . . . . . . 155 21. pH of mud and limestone requirements . . . 156 22. Rate of stocking of ponds and expected yield per acre per year . . . . . . . . . . 165 23. Annual rate of growth in weight of some cultivated fishes . . . . . . . . . . . . . 173 24. Development of swamps for fish culture in East Pakistan . . . . . . . . . . . . . . . 187 25. Results of experiment on rice-cum-fish culture in Bengal in 1945 . . . . . . . . . 193 26. Chemical analysis of the soil of a typical Bheri . . . . . . . . . . . . . . . . . . . 202 ix Figure Plate II. LIST OF ILLUSTRATIONS Page Map of Pakistan showing the location of East Pakistan and West Pakistan . . . FrontiSpiece West Pakistan inland fisheries map, 1962 . . . . . . . . . . . . . . . . . . . . 11 General construction drawing of a drifting gill net . . . . . . . . . . . . . . . . . . 34 .General construction drawing of a bottom- set gill net . . . . . . . . . . . . . . . . 34 A diagrammatic presentation of food chain in a fish pond starting with macrophytes . . 74 A diagrammatic presentation of food chain in a fish pond starting with microscopic algae . . . . . . . . . . . . . . . . . . . 74 Map of East Pakistan Showing the districts, the Sundarbans and the major fresh-water rivers . . . . . . . . . . . . . . . . . . . 121 Fresh-water food fishes of Pakistan a. Catla catla Hamilton b. Labeo calbasu Hamilton c. Cirrhina mrigala Hamilton d. Barbus tor Hamilton . . . . . . . . . . 237 Fresh—water food fishes of Pakistan a. Labeo nandina Hamilton b. Labeo gonius Hamilton c. Labeo rohita Hamilton d. Lates calcarifer Bloch . . . . . . . . . 239 Plate III. IV. VI. Fresh-water food fishes of Pakistan (DCLDU'SD Ophicephalus marulius Hamilton Ophicephalus punctatus Bloch Anabas testudineus Bloch Wallago attu Bloch and Schneider Saccobranchus fossilis Hamilton Fresh—water food fishes of Pakistan a. Colisa fasciata Bloch and Schneider b. Ambassis baculis Hamilton c. Notopterus notopterus Hamilton d. Notopterus chitala Hamilton Fresh—water food fishes of Pakistan a. Clarias batrachus Linnaeus b. Clarias batrachus Linnaeus with labyrinthiform accessory reSpiratory organs exposed c. Tilapia mossambica Peters (male) d. Tilapia mossambica Peters (female) Fresh to brackish-water food fishes of Pakistan a. Mugil corsula Linnaeus b. Mugil parsia Cuv. et Val. c. Hilsa ilisha Hamilton xi Page 241 243 245 247 30302: :0in I}, «35...... sh: .fo d V l O 838 in: \«s 3.1m etc—.3. 8.300 2.3.35. 4 .J. 2 . 1.35 A a» o w w v. ~ ~ «can» \d 1 v . W. . .J a d w .: Figure 1 INTRODUCTION Pakistan (Figure l) with an area of 365,000 square miles and a pOpulation of 94 million has considerable fish- ery resources, but these have not yet been properly assessed. A 770-mile coast line, a continental shelf in the Arabian Sea and the Bay of Bengal and a large number of off-shore islands form an extensive access to marine fish, while four large and numerous small rivers, artificial lakes, reservoirs and swamps, and over 300,000 ponds form a rich potential source of inland fresh-water fish. Because of largely prim- itive fish cultural practices, fishing methods and inadequate facilities for preservation, storage, transport and market— ing, fishery resources of Pakistan are not now being fully exploited or developed. Fishing in the seas are generally confined to a narrow belt of three miles and to the rich off-shore islands, hence the deep waters of the seas are left practically unexploited. Vast areas of inland waters remain completely or partially fallow and destructive fish- ing practices are often employed for lack of conservation measures. The total protein content of the diets of the Pakistanis is low when compared with standards commonly accepted in North America and Western Europe; the animal protein content from meat, milk and eggs is even lower (FAO, 1963 ). The place of fish in the Pakistanis’ diet has been estimated by Borgstrom (1961a, 1962a) and is shown in Table 1. Pakistan is more or less a flat country and all its available agricultural land are under the plough. East Pakistan occupies only 15% of the total area of Pakistan but supports 54% of its population which is increasing at the rate of 2.2% per year. The studies by Borgstrom (1961a, 1962a) have further shown how Obligately the Pakistanis are depending on fish protein (Table 2). From Tables 1 and 2 it will appear that the only practical way to improve the diet of Pakistan and to check protein malnutrition in the peOple is through greater use of fish. Fish is approximately 18% protein by weight and is very rich in such amino acids as lysine, methionine and tryptophan which are in poor supply in cereals (Guha, 1962). §33_also Borgstrom (1951) and Finn (1960). Vegetables, rice and fish have been major foods of the Pakistanis for ages. This dependence is not likely to be changed. FAO (1962 ) estimated that Pakistan is 22nd among the fishing nations of the world in terms of total catch. Pakistan caught 336,600 metric tons of fish in 1962, 68% of which came from fresh-water. The production of fresh- water fish from the warm waters of Pakistan is not costly as compared with agricultural production which is now engaging 76% of its population. Production of fresh—water fish can TABLE 1. Fish in Pakistanis' dieta Total Fish meat Calories Animal % of population eaten per in daily protein fish head per diet per head protein annum per day in that (millions) (kg) (g) total 94 4.5 2,130 5.7 38.6 aSource: Borgstrom (1961a, 1962a). TABLE 2. Pakistan's dependence on fish proteina Total % of Additional Extra Extra population population arable milk meat obtaining land needed »needed animal needed to over over protein replace present present from fish fish production production (theoretical (millions) figure) % % % 94 39 6 35.2 137.7 aSource: Borgstrom (1961a, 1962a). be increased several fold if the fisheries are conducted on a scientific basis and all available fresh-water areas are improved, reclaimed or otherwise made suitable for scientific fish culture. It is with this belief that I wish to make a critical study of the fresh-water fish and fisheries and the raising of food fish in Pakistan which will, it is hOped, create interest in, and action from, the fishery biologist as well as the administration in Pakistan. I. THE FRESH-WATER FISH A. The Habitat The fresh-water fish extend from the sea level to the hill ranges in which water exists in sufficient quan— tities. They are found in all rivers and their tributaries, ponds, lakes, reservoirs, swamps and rice fields. Rivers and their expansions are inhabited by fishes, cultivable or otherwise, but ponds, lakes, swamps and rice fields are, and can be, used for fish culture. 1. Rivers and Their Expansions East Pakistan has a network of rivers, the Padma, i Meghna and the Brahmaputra being the three major river sys- tems all flowing through the plains to the Bay of Bengal. The Indus, the principal stream of West Pakistan, descends from the Himalayas and flows through the plains into the Arabian Sea. Rainfall and seasonal changes affect flow, volume and the course of these rivers (Ramdas, 1946), which in turn affect the fishes inhabiting them. Table 3 shows the climatological data of Dacca, East Pakistan, and Lahore, West Pakistan. The Indus has, besides Springs, two prominent sources of replenishment. During the summer months, it receives abundant water from melted ice and snow, and a Assesses .moammo HmOAwoaouoowoz qmpmflxmm on» >9 Coaamanm memo Hmcfimfiuov immaHm>a osoa-oooa .ampmaxam .muonsa new mouse mo «use HegemoaopaERHo .m mamas 0.00 0.00 0.00 00.00 0.05 0.05 0.00 05.05 0000 00 00900 Hmscc< 0.00 0.00 0.05 50.0 0.05 0.50 0.05 00.0 00000000 0.00 0.50 0.00 00.0 0.05 0.00 0.00 00.0 00000>oz 0.50 0.00 0.00 00.0 0.55 0.05 0.00 50.0 0000000 0.00 0.05 0.50 00.0 0.00 0.05 5.00 05.0 000000000 0.00 5.05 0.50 00.0 0.00 0.05 0.50 50.00 00:0=< 0.00 0.00 0.00 00.0 0.00 0.05 0.00 50.00 5000 0.00 0.05 0.000 00.0 0.00 0.05 0.00 00.00 0000 0.00 0.05 5.000 00.0 0.05 0.05 0.00 00.0 502 0.00 0.00 0.00 50.0 0.00 0.05 0.00 00.0 0000< 0.00 0.00 0.00 05.0 0.00 0.00 0.00 00.0 00002 0.00 0.00 0.05 50.0 0.00 0.00 5.00 00.0 50000000 0.00 0.00 0.00 00.0 0.00 0.00 0.55 00.0 5000000 0 . 5000 . 50000000 0 . 0000 . 50000000 0006 :02 x02 000E Game 002 . x02 0008 >Hmmp >0000 000E >aneos >0000 >0000 0008 >ancos >uwoflesm 00000000809 Hammcwmm >000080m 00000000808 Hammcwmm £0002 000m 5Nnn00>00 000 800m pamwms 0.00000--000000000 n200000.0300000 000m Nonn100>00 000 800% unmwmn 0.00005--000000000 “2.00000--00000000 Acmpmflxmm «mmzv 000000 Acmumfixmm pmmww spam daily rise and fall in the amount of water can be observed. Throughout the monsoon season, the rains hasten the melting of snows. Thus, with the beginning of March the Indus floods, the inundations resulting more from the melting snows than from the rains as are in the rivers of East Pakistan. The Indus forms torrents, rises and subsides rapidly especially during the rains. As this river has few contiguous oxbow lakes in which the fish can escape floods, the fish existing there must have adhesive organs, deeply forked caudal fin and very streamlined bodies which are not found so prominently in those inhabiting the East Pakistan rivers. During the cold season, the Indus, unreplenished by rains or melted snows, becomes, in places, quite small. The rivers of the plains of East Pakistan are, of course, chiefly the continuations of those descending from the hills, but the diurnal fluctuation in the water level is scarcely apparent as they are far away from their sources, and these always have a fair supply of water.i The rivers in the hills as well as on the plains have a poor supply of water throughout the winter months. The south-west monsoon begins in June and the Indus reaches its highest levels in August, subsidence begins in September commonly being completed in November. The East Pakistan rivers overflow soon after the monsoon. During these periods of floods, the oxbow lakes receive a fresh supply of water. Thus the "dhands" (lakes) of Sind receive water from the Indus (Figure 2). The dhands are of two kinds: (1) isolated dhands which are in communication with the Indus only during the periods of floods and are mostly dried up before the next year's supply; and (2) connected dhands which are the expan- sions of a river, small stream or canal, are, throughout, or for the most part of the year, connected with running water (Day, 1873). The Punjab with all its small rivers and irrigation canals possesses important fishing waters (Figure 2). There is no reliable inventory of waters suitable for fish culture in Pakistan. Table 4 gives an estimate of its cultivable inland waters (Schuster, 1951; Anonymous, 1952; Hora and Pillay, 1962). B. Taxonomy and Distribution The important fresh-water food fishes belong to the order Physostomi and eSpecially the families Cyprinidae, Siluridae, Ophicephalidae and Clupeidae. Some are also found in the order Acanthopterygii (Weber and de Beaufort, 1911- 1936; de Beaufort, 1940; Day, 1958). Other orders of fresh— water fishes are used as food by the poorest inhabitants only, or are entirely rejected. A comprehensive list of the fresh- water food fishes of Pakistan is given in the Appendix which will give an idea of Pakistan's piscine wealth. Most of the important food fishes are common to both parts of Pakistan with the exception of a catfish (Clarias batrachus) from West 10 Figure 2. West Pakistan inland fisheries map, 1962 11 _ . __1_..__._ _.___~._.___—_y.———_——_-. WEST PAKISTAN .1 I IN I. A N D /-/‘TT;>“) FISHERIES MAP (1 "a... ........ 0000 M- ness usufl. . ' mufl'fix/y 7.. ' OAIOAIAI r/’ ‘ .... u. IMHLM km 0- mm ‘L “um: uu ’ Out A emu“. AHAVALPU / \ E: . I ‘ A mean?“ U / \ _ Isl-Ivanlun I - x A L A r j 3“. I ‘ I — ' ( ." KHAIR' \fl' - ucmc“ \ . \i I N D I A . use ( uneven ./—~‘ . uu ' °'. . c- rune lulu \. / .‘ z 'i ulnar? Illlll OIL! .' M ;' 1., "- um ’3 ‘ E, Aa-u k I. I I C C L . :1“, H Y D E ‘ . ‘ D \ ._ EV _ _ \ 5 00...... VI Revenues I 'HIH‘CNI ”r. - 0.. O H...” A nun ‘ » . . 1 . . 0. ~ \ LS0 nus O “I; / .0.-. .0 -__._-.. -____ V0,) fi’Y'j‘.‘ L", ‘ Flv runs no sun cu. \'P£$ ;-i I ‘ 3'. C.-___..._.__.._.-...... -0 -- - — 0a 4 \040 I _::;111__1,,41 R48“ “\ summits omens: i 4'. 4 .\ a ._.1-_- __. . .— . ___.._., NSF \ I fit“ nuns -/..- _/ nuvtns 2.51,: stvcmuu ounos A Figure 2 12 TABLE 4. Estimated area of cultivable inland waters of Pakistana Category 0.331..) Fish ponds Fresh-water 105,000 Brackish—water 24,000 Natural lakes . . . . . . . . . . 30,100 Artificial lakes, reservoirs, channels, etc. 68,500 Salt or mangrove marshes suitable for fish culture 305,200 Lagoons and estuarine waters suitable for fish culture 424,000 Riceafields Without fish culture 43,400 With fish culture 12,000 Total inland waters 1,012,800 Arable land 21,000,000 Total area of country 94,300,000 %»of cultivable inland waters to total area of country . . . . . _A_ 1. aSources: Hora and Pillay (1962); Schuster (1951); Anonymous (1952). bOne hectare = 2.2 acres. 13 Pakistan (Ahmad, 1953). The important food fishes of the tWO provinces (East Pakistan and West Pakistan) include the carps (Catla, rohu, mrigal and kalbaus), the catfishes (Saccobranchus fossilis, Wallago attu, Mystus aor and Silonia silondia), the snakeheads (Ophicephalus Spp.), and the featherbacks (Notopterus spp.). Among the most important estuarine food fishes that frequent the fresh-waters of Pakistan are the hilsa or shad (Hilsa ilisha), perch (Lates calcarifer) and the mullets 012331 spp.). Fishes that inhabit the fresh-waters of Pakistan are either migratory or non-migratory. Some of the migratory species such as mahsir (Barbus tor) of West Pakistan ascend the hill streams from the rivers of the plains for breeding purposes whereas others which never leave the plains may sometimes be estuarine such as Hilsa ilisha. Others are entirely fresh-water species such as carps. Migrations in adult fish are effected for breeding, predation or to obtain food. Among the non-migratory fishes are the loaches and small catfishes of the hill streams and the ambassids such as Ambassis baculis of the plains. The majority of the breed- ing fishes are polygamous but some are monogamous such as the snakeheads. The breeding time varies with seasons and local- ities. The migratory ones almost invariably select the mon- soon time (June to September). 14 The carps belong to the family Cyprinidae. They have no teeth in their jaws but carry them on their inferior pharyngeal bones. None of them has more than one dorsal fin. They are grouped in three sub-families (Day, 1873): l) Cobitidinae or the little roaches extend through- out Pakistan's fresh-waters, from sea level to many thousand feet elevation, even breeding in places where the rivers are almost entirely replenished by melting snows. Loaches such as Nemacheilus sp. are excellent food for the larger fishes and are also esteemed by the peOple. Their air—vessel is more or less enclosed by bone. 2) Homalopterinae or sand grubbers have no air- vessel, are insignificant in number and size, and reside under stones in streams along the bases of hills or at moderate el- evations. 3) Cyprininae or true carps are widely distributed and are the most important food fishes. Their air-vessel is not covered by bone. These carps are divisible into those of the hills and those of the plains. The hill carps again can be subdivided into those which permanently reside there and those which are occasional or periodical visitants that ascend for breeding or a change in their food. The non- migratory hill carps like Oreinus sinuatus are an important article of food there for the resident population. The migratory hill Carps are those which breed in small streams of the hills but descend to the rivers of the plains where 15 they reside during the cold and dry months of the year when the small hill streams would be unsuited for their residence because they either dry up at this time or do not support sufficient food. They reascend to the base of the hills dur— ing the summer months and with the first burst of the monsoon return to the hill region (example, Barbus tor). Among the carps of the plains are a very large and varied number of Species some of which are migratory while others are not. These migrations are mostly effected for breeding purposes and generally take place during the south- west monsoon. The finest carps belong to the genera £2233, Cirrhina and Catla which will be referred to as the major carps. The fishes belonging to the family Siluridae are commonly known as catfishes. They have a number of barbels arranged around their mouth. They prefer muddy to clear water. The more developed and numerous these barbels are, the better they are adapted for an inland and muddy fresh- water habitat. Catfishes are scaleless and are generally armed with serrated Spines in the dorsal and pectoral fins with which they may inflict severe wounds. The large muddy rivers of East Pakistan are very well—suited for the cat— fishes (Hora, 1934). The fresh—water catfishes may be divided into those of the hills and those of the plains; the former being small in size and often possessing a thoracic adhesive apparatus to 16 enable them to adhere to rocks and thus prevent their being carried away by the descending torrents. The catfishes of the plains are very numerous, existing in almost every piece of fresh—water while the larger rivers contain some such as Pangasius pangasius, Wallago attu, and Bagarius bagarius. None of these possesses any adhesive apparatus. The snakeheads belong to the family Ophicephalidae. They are considered excellent food in the Punjab, West Pakistan (Khan, 1934). The herring family Clupeidae furnishes examples of both migratory and non-migratory Species in the fresh-waters. Among the migratory herrings, the best known is the hilsa (Hilsa ilisha). It ascends the fresh-water rivers for breed- ing during the monsoon. The non-migratory herrings such as Gadusia chapra live and breed in ponds and lakes. The percomorph fishes are not found in any great num- bers in the inland fresh-waters. They are more abundant in the coastal districts than far inland. Among the perches are Anabas testudineus, Colisa fasciata, Nandus nandus, Lates calcarifer, Mugil spp. and some others. C. Respiration of Fresh:water Fishes Fish generally breath through gills. A number of food fishes such as the catfishes (Clarias batrachus and Saccobranchus fossilis), the climbing perch (Anabas testudineus), and the snakeheads (Ophicephalus spp.), live 17 in pools and marshes. They have developed remarkable air- breathing systems. Lack of oxygen in the shallow tropical waters must have been responsible for the evolution of such an air-breathing habit. Their complicated accessory reSpir- atory organs point to the same conclusion. It is a well-known fact that in the animal kingdom the area of respiratory epithe- lium is increased in waters deficient in oxygen. In the dry season the water of pools and marshes becomes stagnant, and, as a result of putrefaction, the oxygen is gradually reduced till, in some cases, the water becomes almost totally devoid of oxygen. In these circumstances, the fish, if they are to survive, must develop increased reSpiratory surfaces (Das, 1928). These may develop as outgrowths either of the phar- yngs or the opercular cavity as in Clarias batrachus (PLATE V). Table 5 shows the air-breathing organs of some fishes of Pakistan and the method of their blood circulation (Carter, 1957). See further Fry (1957). The young of Anabas, Clarias and Saccobranchus liv- ing in clean water are pure water-breathers. Their air- breathing habit is developed only when the growing fish begin excursions out of the water in pursuit of prey or in search of new ponds. The air-bladder of Clarias and Saccobranchus is very much reduced and degenerate in the adult stage. Snakeheads (Ophicephalus spp.) can breed in foul water and the young gulp air from the beginning. Experiments (Das, 1928) have shown that the snakeheads die if deprived of 18 TABLE 5. Air-breathing fishes and their blood circulationa Name of fish Air-breathing Blood circulation organ Afferent Efferent Ophicephalus Pharyngeal Aortic Jugular epithelia arches vein Clarias Epithelia of Afferent Efferent branchial arches arches chamber Saccobranchus Epithelia of Afferent Efferent branchial arches arches chamber Anabas Epithelia of Efferent Jugular branchial arches vein chamber a Source: Carter (1957). 19 access to the air even when they are kept in water saturated with oxygen, According to Hora (1935), the habit of air-breathing has developed along two distinct lines: (1) by an increase of reSpiratory surface for aquatic respiration and direct contact with the air afterwards, and (2) by surfacing to get the better oxygenated water and then taking in occasional gulps of air and passing it over to the gills. In either case, the stimulus is supplied by the lack of oxygen in the water. II. THE FRESH—WATER FISHERIES The fresh-water fisheries of Pakistan may be clas- sified under the following categories: (1) carps, (2) cat- fishes, (3) live fishes (snakeheads and perch), (4) feather— backs (Notopterus spp.), and (5) eels. Carps account for nearly 40% of the total fresh-water catch being closely followed by catfishes. -Among the anadromous fisheries, the hilsa (Eiléi ilisha) (PLATE VI) provides the most important single fishery of particularly East Pakistan. A. Production The magnitude of fresh-water fisheries can be ascer- tained from the catch and landing statistics. Collection of fishery statistics is still in its infancy in Pakistan. Table 6 gives an estimate of Pakistan‘s catch of fresh- water fishes which come mostly from East Pakistan. Catch statistics of hilsa are available in Pakistan since the beginning of the hilsa investigation project in 1955 (Table 7). Hilsa is available in East Pakistan throughout most of the year. Except for the Rivers Brahmaputra and Tista which have rapid currents, hilsa ascends several hundred miles inland (Ahmad, 1954). There are two runs, one in 20 21 TABLE 6. Catch of fresh-water fish in Pakistana Total Fresh-water Year catch catch % Fresh—water 1,000 metric tons 1948 na 8.5 _-_- 1955 270.9 169.0 62.4 1956 277.0 168.9 61.0 1957 282.8 191.2 67.6 1958 283.7 192.3 67.8 1959 290.1 196.3 67.7 1960 304.5 195.0 64.0 1961 319.1 216.6 67.9 1962 330.6 na ____ aSource: EAO.(1962); na = not available. 22 TABLE 7. Catch of hilsa in Pakistana Province 1955 1958 1959 1960 1,000 metric tons East Pakistan 20.0 20.0 20.0 15.0 West Pakistan 2.0 3.0 1.0 0.9 Total 22.0 23.0 21.0 15.9 aSource: Anonymous (1961). 23 winter and the other during the monsoon, the latter provid- ing the bulk of the total catch. In West Pakistan, only the River Indus supports a hilsa run (Qureshi, 1954). The run starts from the middle of February and ends in mid-October; the peak season being reached from May to July. There are about 150 miles of hilsa fishing area of Sind (s33 Figure 2). Preliminary investigation conducted on the popula- tion of hilsa shows that there is only one species in the Indus and that there are probably two races in the rivers of East Pakistan (Pillay, 1952; Anonymous, 1961). The information on the migration of hilsa is largely based on the observations of fishermen's catches. Day (1873) concluded that hilsa were anadromous in the Gangetic rivers and stated that the fish spends a part of its life in the sea, not far from the shallow coastal belt. Prasad (1919) doubted whether it is truly anadromous as it is found in the rivers throughout most of the year. Hora (1938) ob- served that it rarely goes into the sea and supported Prasad's (1919) contention that it is not a truly anadro- mous Species. Naidu (1939), however, maintains a reverse opinion. Hora and Nair (1940) studied the young hilsa (Jatka) of East Pakistan and stated that they are two to five months old when they migrate from estuaries into fresh-water for feeding. Naidu (1939) and Pillay (1955) believe that Jatka 24 hilsa belong to a distinct stock and their ascent of the rivers in January and February is for spawning. Spawning takes place in the tidal waters and in the middle reaches of large rivers. Floods and sexual maturity induce the fish to undertake the upward migration (Hora, 1941). The extent of migration of hilsa differs greatly in various river systems of Pakistan. In East Pakistan, they migrate several hundred miles up from the mouth of the rivers. Hilsa was not available in the upper reaches of the Rivers Padma and Jamuna (specially in the northern region) prob- ably due to Silting and construction of a dam. East Pakistan rivers carry about one billion metric tons of silt every year. Prior to the construction of the Ghulam Muhammad (G;M.) Dam over the Indus in 1955, hilsa ascended to the Sukkur Dam (see Figure 2), 100 miles farther up on the same river, but now it is restricted by the G.M. Dam only, a distance of 150 miles from the mouth of the river. The decline in the catch of hilsa (70%) in the River Indus from 1958 to 1960 (Table 7) is believed to have resulted from the construction of the dam. Day (1873) considered it essential to provide fish passes to facilitate the migration of hilsa to the upper reaches of rivers in which artificial obstruc- tions have been constructed. Observations made on fish passes provided in the G.M. Dam indicate that hilsa does not negotiate them (Anonymous, 1961). It appears desirable that detailed studies like the researches on anadromous fish 25 passes at dams by Collins (1954) and Collins and Elling (1960) in the United States be carried out to determine how seriously they threaten the existence of the hilsa fishery because many more dams will result in future from the devel— opment of water resources for power, irrigation, navigation and flood control, and to determine ways to help it going up the dams for breeding. For a comprehensive treatise on fish- wayS and other fish facilities see Clay (1961). In reSpect to fresh-water fish production, Pakistan is fifth among the world’s fresh—water fish producing nations, as Shown in Table 8. B. a.ssu..-.I0\ ~_§d\\ 26 .0000000>0 000 u 00 "Anmooav soupmmuom 0000:0m0 0.0 0.0 0.00 0.005.0 0.0 0.00 5.000.0 0.0 0.00 0.005.0 .0.0 0.0 0.00 0.05 0.000 0.50 0.50 5.000 0.00 0.00 0.000 00000000 0.0 00 00 00 0.00 0.500 0.000 0.00 0.000 0.000 00000 5.0 00 00 00 00 00 00 0.00 0.000 0.000 00000000 0.0 0.00 0.000 0.000 5.50 0.000 0.000 0.50 0.000 5.000 20000000 0.0 0.00 5.000 0.000.0 0.00 0.000 0.000 0.00 5.000 0.000.0 00000 0.5 00 00 00 0.00 0.000 0.005 0.00 0.000 0.000 000000000 0.00 0.00 0.000 0.000.0 0.00 0.000 0.005.0 0.50 0.000 0.000.0 000: 0.50 0.00 0.000.0 0.000.0 0.00 0.000.0 0.000.0 0.00 0.000.0 0.000.0 00000 000 0.00 0.050.0 0.005.50 0.00 0 000.0 0.000.00 0.00 0.000.0 0.000.00 00003 00:0000 00003 00003 00003 00000 unmmum 00003 unmoum 00003 unmoum 00003 00003 $ unmoum 00008 g unmoum 00009 0 unmoum H0008 500:000 00 0 0000 0000 0000 II 00000 000000 000.00 0oooanwmoa .000000300 000000000 :0 0000030000 000% 00003nmoum .w mqm0 000.0 000.0 .00000 000.0 000.0 000.0 0000 0-0 000.00 000.00 000.00 000.00 000.00 050.00 000 0 0000: ”00000 300 000 000m 000.50 000.50 000.50 000.50 005.00 000.50 000.00 000.00 000.00 000.00 000.00 050.00 000000000 000000 000.00 000.00 000.00 000.00 000.00 000.00 000000000 000000 055.00 500.00 000.00 050.00 005.00 000.00 0000000000 00000 0000 0000 0000 5000 0000 0000 00000000 .00000000 0mmoa 00000 00000x0m mo 00000 mcwnmfim 00003unm00m p 000050 000000000 000.0 00 0:00> 00000 mo 00063: > z .o mqmonm may mo 2 m\pfiom ocflsm .mE mo cofipmeflwmm 629 How Asmoav Ocm8mu93mmamm “Aamoav mafiaaom can xooamp .Ammoav .H0 00 easememansmmamm ”n0moav x0Mu .AmmOflv mamaaaaz .Awmaav snowewmm D H.0 H.k no.0 0.5 0.5 40.0 meaflm> 0.0 0.0 00.m 0.0 m.0 em.m meamocae 0.0 m.H 0o.H 0.4 e.H H0.o canaouasus k.m 0.0 00.0 0.0 0.0 0H.m meflcomuea 0.0 0.0 00.0 0.0 0.0 00.0 mcaamamascmnm 0.m 0.0 00.m H.e m.m m0.m 020:000002 0.H 5.0 ma.oH m.k H.w ms.o meflmsq 0.5 0.0 0H.0 m.0 0.HH me.0 mcaosma m.e 0.0 km.0 0.0 0.0 00.0 0:00:0H00H m.m H.m 00.0 H.m e.m m0.m meauapmfim o.m 0.0 00.0 0.0 0.0 km.w mcacfiwu< . . . . . . . . . . . . cfiowoud .m ooa\pmom cumEm m . . . . . . . . . . . . mascamv nomuafiav mmfipmnsv Amflonav noHonzv A:00HHOQ 00000: umuam nmmmm «mum m.emm meafls 0.300 man0000.mmfim cage oeaa< mmmzpmpoom Honuo meow £903 swam mo unopcoo Ufiom OGflEm Hmflpcommo mo comMquEoo .NH mqm** Cyprinidae Catla catla Hamilton F I Labeo rohita Hamilton F I Labeo calbasu Hamilton F I Labeo fimbriatus Bloch F I Barbus sarana Hamilton F I Barbus chola Hamilton F I Cirrhina mrigala Hamilton F I Cirrhina reba Hamilton F I Cyprinus carpio Linnaeus F E Carassius auratus Linnaeus F E Siluridae Wallago attu Bloch and Schneider F I Clarias batrachus Linnaeus F I Saccobranchus fossilis Bloch F I Ophicephalidae Ophicephalus marulius Hamilton F I Ophicephalusgpunctatus Bloch F I Ophicephalus striatus Bleeker F I Anabatidae Anabas testudineus Bloch F I OSphronemidae Trichogaster pectoralis Regan F I Colisa fasciata Bloch and Schneider F I Cichlidae Tilapia mossambica Peters F E Mugilidae Mugil tade Forskal B I Mugil parsia Cuvier and Valencienns B I Mugil cephalus Linnaeus B I Mugil corsula Linnaeus B I Latidae Lates calcarifer Bloch B I * . (F) = Fresh—water; (B) = Brackish-water. **(I) = Indigenous; (E) = Exotic. 8O Labeo fimbriatus Bloch This is another fresh-water river carp attaining a maximum length of 900 mm. and weight of 4500 g. It Spawns like 93313 in rivers during the monsoon. Spawn collected in rivers are raised in ponds. They are plankton and detritus feeder. Barbus sarana Hamilton This is also a fresh—water river carp attaining a maximum length of 760 mm. It Spawns like 92313 in rivers during the monsoon. Spawn is collected in rivers and raised in ponds. They are plankton and detritus feeder. Barbus chola Hamilton This is another river carp attaining a maximum length of 260 mm. Other characters of this fish are not reported. Cirrhina mrigala Hamilton (PLATE I, c) This is another fresh—water river carp attaining a maximum length of 1,000 mm. and weight 4,000 g. It breeds in rivers during the monsoon. The eggs hatch in about 18 hours after fertilization and adult characters are attained in three weeks. It iS omnivorous. Cirrhina reba Hamilton This is another fresh—water river carp attaining a maximum of 300 mm. It breeds in rivers like Catla. The eggs measuring 2.8-3.2 mm. in diameter hatch about 15 hours after fertilization. Spawn is collected in rivers and 81 raised in ponds when fry of major carps are unavailable. It attains sexual maturity within a year. It feeds on plankton and detritus. Cyprinus carpio Linnaeus It is a fresh—water exotic carp. It is being cul- tured experimentally in East Pakistan. It spawns in con— fined waters at the beginning of the monsoon. The eggs are yellow and adhesive and are laid on aquatic plants. They hatch in about two to three days. It is omnivorous. Carassius auratus Linnaeus It is another exotic fresh-water carp attaining a maximum length of 450 mm. It can breed in ponds or other confined waters throughout the year. It lays adhesive eggs on aquatic plants which hatch within four days. It is pos- sible to cross it with Cyprinus carpio. It feeds on plank- ton and detritus. Wallago attu Bloch and Schneider (PLATE III, d) This is a fresh—water catfish attaining a maximum length of 1,500 mm. It Spawns during the monsoon in rivers and channels. The eggs measuring 1.2—1.5 mm. in diameter hatch in about 17 hours. It has an extremely carnivorous habit and is unfit for culture with carps. It is reared in swamps and marshes. Clarias batrachus Linnaeus (PLATE V, a and b) It is another fresh-water river catfish attaining a maximum length of 400 mm. It breeds in confined waters throughout the year. It often occurs as extraneous fish in 82 ponds, lakes, swamps and rice fields. It has labyrinthiform accessory respiratory organs and can withstand very low oxy— gen concentration. It is omnivorous. Saccobranchus fossilis Bloch (PLATE III, e) This is another fresh-water catfish attaining a maximum length of 450 mm. It breeds in ponds and other con- fined waters throughout the year. It also occurs in ponds as extraneous fish. It can withstand, like Clarias batrachus, extreme conditions such as low concentration of oxygen (i.e., less than 2 p.p.m.). It has accessory reSpiratory organs like those of Clarias. It is omnivorous. Ophicephalus marulius Hamilton (PLATE III, a) This is a fresh-water snakehead fish attaining a maximum length of 1,200 mm. During the monsoon, it breeds freely in ponds and swamps. The eggs measure 1.5 mm. in diameter. The young become independent of parents in about six weeks. It is carnivorous. Ophicephalus punctatus Bloch (PLATE III, b) This is another fresh-water snakehead fish attaining a maximum length of 300 mm. It breeds in ponds and rice fields during the monsoon. It builds nest and gives parental care to the young. It can live in water with low oxygen con~ centration with the help of accessory reSpiratory organs. It is carnivorous. 83 Trichogaster pectoralis Regan It is a fresh-water gouramy which breeds and grows rapidly in rice fields. It attains a maximum length and weight of 250 mm. and 140 g. reSpectively. Its eggs hatch within two days. It is a plankton and detritus feeder. Colisa fasciata Bloch and Schneider (PLATE IV, a) It is also a fresh-water gouramy. It is larvivorous in habit. Its other characters are not reported. Tilapia mossambica Peters (PLATE V, c and d) It is a fresh—water exotic fish belonging to the family Cichlidae. It attains a maximum length and weight of 300 mm. and 450 g. It breeds in confined waters prolifically throughout the year. The male fish builds nest at the bottom of the pond and the female lays 75 to 250 eggs. The eggs are taken into the mouth of the female as soon as they are laid. They hatch in three to five days. It can also be cultured in brackish-water ponds (Chacko and Krishnamurthi, 1954; Chen, 1953; Chimits, 1955, 1957). It is a plankton feeder. .Mugil tade Forskal It is a brackish—water mullet which is easily adapt— able to fresh-water ponds. It attains a maximum length of 700 mm. It does not breed in ponds. Its fry are collected from coastal waters and raised in ponds. It is herbivorous. Mygilparsia Cuvier and Valencienns (PLATE VI, b) It is another brackish-water mullet easily cultiva- ble in fresh and brackish—water ponds, lakes and swamps. 84 Like M. tade it does not breed in confined waters. Its fry and fingerlings are collected from estuaries. It attains a maximum length of 400 mm. in ponds. Mugil cephalus Linnaeus It is another mullet which is cultured in brackish to fresh-water ponds. It attains a maximum length and weight of 500 mm. and 1,300 g. reSpectively. It also does not breed in confined waters. Its fry are collected from estuaries from December to March. It is a plankton feeder. Mugil corsula Linnaeus (PLATE VI, a) It is also another mullet cultivated in ponds in coastal districts. It attains a maximum length of 450 mm. It Spawns in rivers during the monsoon; its eggs are pelagic and semibuoyant and measure 1 mm. in diameter. It is herbiv- orous. Lates calcarifer Bloch (PLATE II, d) It is a brackish-water perch attaining a maximum length of 1,700 mm. and weight of 5,000 g. It often occurs as extraneous fish in ponds in coastal districts. It does not breed in ponds. The fry are collected from rivers, creeks and lagoons. It is extremely carnivorous. l. Breeding Habits and Requirements Some cultivated fish Show parental care, others do not. The snakeheads, the gouramis and some catfishes like N Mystus aor build nests and guard the young. Tilapia pro- tects its eggs in the buccal cavity. Fish showing parental 85 care do not Show high fecundity and some such as Tilapia breed thrice a year. Their progeny have a high rate of Sur— vival; while fish, such as the major carps, Showing no paren- tal care, have high fecundity in order to compensate for the loss of the eggs or the young due to predation or other natural causes (Table 14). According to Hubbs and Eschmeyer (1938), the follow— ing conditions have been found favorable for Spawning of lake fishes: A water level stable enough to avoid drying of eggs or fry or subjecting them to either abnor- mally shallow or deep waters. A water level which covers the Spawning grounds to a proper depth, whether these grounds be grav- el bar or bulrush patch or a marsh. Favorable chemical conditions in the water cover— ing the Spawning beds, particularly a high con— tent of dissolved oxygen. Relatively constant temperature, not rising high enough to harm the eggs and not dropping low enough to kill the fry or to drive the fish off their beds before the Spawning or the guarding of the eggs is completed. Temperature low enough or high enough (depending on the Species involved) for the fish to Spawn normally. 86 TABLE 14. Comparative fecundity of some major carps Name of Total Number of Ratio of Reference Species weight eggs number produced eggs to total weight of (g) (1,000) Species Labeo rohita 4,653.5 1,905.0 409.3 Khan (1934, 1947) Labeo calbasu 1,816.0 739.4 409.3 Khan (1934, 1947) Labeo bata 1,049.9 300.0 285.5 Alikunhi (1956) Cirrhina mrigala 1,475.5 216.8 146.9 Khan (1934) Catla catla 5,107.5 400.3 78.3 Khan (1934, 1947) 87 Waters relatively free from smothering silt, whether caused by waves and currents, by motor boats or by wading. A coating of Silt is harm- ful to fish eggs. Spawning beds relatively free from disturbance by motor boats or bathers. Protection from fishing during at least the height of the Spawning season, and A sufficient area of the prOper bottom material to deposit the eggs, at suitable depths and in places adequately protected from wave action. AS already mentioned, the cultivated carps of Pakistan do not breed in confined waters. They breed in fresh-water rivers during the South-West monsoon from June to September. Ahmad (1945a, b), Hora (1945a) and Khan (1942) observed that the monsoon flood is the principal determining factor in the Spawning of carps. Keeping in view the observations of Hubbs and Eschmeyer (1938), the following observations may be made on the effects of floods on the Spawning of Pakistan's major carps. a. A heavy flood indicates more or less that the monsoon conditions have set in properly and that a water level stable enough to avoid drying the eggs has been established in the marginal areas where the Spawn is liberated. 88 The flood also ensures that the actual breeding grounds have been covered to a Suitable depth. Rushing water after a torrential rainfall will also ensure a high content of dissolved oxygen in the water covering the Spawning beds. It has been observed experimentally (Hora, 1945a) that the temperature of water in which the brood fish are kept may rise high but after a heavy shower, the temperature comes down and then the fish begins to Spawn. For a considerable period after a heavy shower, the temperature remains relatively constant, not rising high enough to harm the eggs and drOpping low enough to kill the fry or to drive the fish off their beds be— fore Spawning. The optimum temperature at which the carps Spawn has been observed to be between 75 and 86oF (23.9 and 30.00c). Silt—laden waters do not appear to be inimical to the Spawning of carps and though the fertilized eggs Sink to the bottom, the larvae hatch within 15 to 20 hours and come to the surface. Besides, in flowing waters, the eggs roll about and do not get covered with Silt. In the Spawning beds of the rivers there is practically no disturbance to the Spawners. 89 h. The migration of Spawners to the shallow Spawning beds exposes them to attack by enemies, including man, and it is desirable from the standpoint of fishery management that the brood fish should be protected during this period. i. For an increased production of fry, it is neces— sary that the spawning grounds should be improved artificially and that a sufficient area of proper material should be made available to the Spawners. From the above, it will appear that indigeneous fishes are adapted to the monsoon floods and other topographical, chemical and physical conditions encountered in the environ— ment. In the Punjab, West Pakistan, the fishes did not breed during the years when rainfall is either untimely or insufficient to flood the grounds (Khan, 1942). 2. Possibilities of Artificial Propagation AS the important cultivated fishes of Pakistan Spawn in the rivers, the fish farmer depends on the timely avail- ability of the stocking material. (The term "stocking mate- rial" denotes the earliest develOpmental stages such as Spawn, fry or fingerlings with which the entire culture operations are started.) Besides, much effort is necessary to collect, sort, condition and transport the stocking mate- rial to the fish farmers. If the fish could be induced to Spawn in ponds or other confined waters by providing them 90 with Optimum hydrological or ecological conditions, the pro— curement of the stocking material could be greatly Simplified. Considerable success has been achieved in this respect with regard to common carp and gold fish. £3313, rohu, mrigal and kalbaus do become sexually mature in confined waters but do not Spawn for want of essential stimuli. Cultivated Species like salmon, trout and the Chinese carps can be stripped to obtain the eggs and milt, but this is not so with Pakistani carps. The secretion of the pituitary gland of the fish has been found to induce ovulation and Spawning. Clemens and Sneed (1962) observed that ripe females of most Species of fish reSpond to pituitary injections by Spawning within 12 to 20 hours, so that it is possible to predict rather accurately when a Spawn will occur. This prediction allows the fish culturist to plan his work according to rigid Schedule, since the injections, to some degree by-pass the variables in the environment, such as rain, flood, tempera- ture and light. Since both males and females reSpond pos— itively to pituitary injections, most Species can be hand- stripped, a practice which offers additional advantages. Culture ponds can be stocked with eggs and fry of uniform size and age. Since the brood stock is not in the pond with the progeny, the possibility of transmission of disease from the brood stock to the offspring is minimized and the predation, if any, by the parent is eliminated. Hybrids 91 can also be produced whenever hybridization is desirable and feasible. Wild fish that have not yet been domesticated may be Spawned more easily by the pituitary method. Frequent— ly, more uniform Spawning has been achieved by the injection of pituitary materials into ripe fish which, because of some environmental or physiological condition would fail to Spawn without such treatment. Russian (Gerbil'skii, 1941; Detlaf and Ginzburg, 1954) and Brazilian (de Menezes, 1954; Fontenele, 1955) fish workers have applied the pituitary method to the large—scale Spawning of Acipenser Sp. and Prochilodus spp. reSpectively. Today the Russians obtain all sturgeon eggs for culturing from pituitary-treated fish (Gerbil'skii, 1957). Pickford and Atz (1957) and Atz and Pickford (1959) Observed that (1) fish pituitaries contain hormones to pre— c3iII>itate Spawning in ripe fish; (2) there is little, if any, Specificity in the hormone of fishes, i.e., the pituitaries of one family or species are usually active in unrelated Species (female .Cyprinus carpio, however, responds to pitu— i1:arties only from the same Species (Clemens and Sneed, 1962)); C 3) there are a number of examples in which gonadotrophic materials from other vertebrates were found to be active in fiSh; (4) out of season Spawning has been induced by the administration of gonadotropins; (5) fresh acetone dried, or frozen pituitaries as well as glycerin, salt and water extracts of pituitaries have Similar activities; (6) under 92 most experimental conditions the injection of pituitaries does not decrease fertility; (7) increased or decreased ex- posure to light (depending on species involved) may have the same effect on sexual development and Spawning as pituitary :injections; (8) lack of reSponse in some experiments with nrammalian gonadotropins may be due to the fact that the dos— zigge was too low; (9) there is little or no qualitative dif— ifeerence in the pituitaries of the male or female donor fish, za‘t’ least from the practical point of view; and (10) there may be seasonal difference in the biological effect produced tDjV’ pituitaries taken from fish prior to Spawning and those ‘t:21111fined waters and thereby ensure a dependable source of Cllléllity fish is being greatly felt in Pakistan today. The f.irst attempt in this work was made by Khan (1938) who tried 13C) .induce Spawning in Cirrhina mrigala by injecting the 51111263ri0r lobe of mammalian pituitary gland into the fish. Akl3tlnough ovulation took place, the treated fish did not SpaWn and the stripped eggs could not be fertilized. Since 1:r“311 no work has been done in this field in Pakistan. In ]:rufl¢ia, however, Ramaswami and Sundarraj (1956, 1957a, b) IlarV13 become successful in inducing catfishes (Heteropneustes C§mbranchu59 fossilis and Clarias batrachus) to Spawn by horrnone injections. Alikunhi et a1. (1960) injected intra- IDeI’itonially the alcohol preserved pituitary material of 93 Labeo rohita (sexes mixed) in three Species of carps namely, Labeo rohita, L. calbasu and L. bata. The successful doses varied from 1.5 to 4.0 glands for L. rohita, 0.33 to 1.0 for 1,. bata and 0.5 for L. calbasu. Two injections, sometimes (Jne, were enough to induce Spawning within a period of 7-12 IIC)urS. Chaudhury and Alikunhi (1957) and Chaudhury (1960) 1‘61ported successful Spawning of Labeo rohita, Cirrhina rn:rxigala, C. reba, and Barbus sarana by intraperitonial pitu— i.t:21ry injection. Partial success was achieved in the case ()1? (Catla catla and Labeo bata. Glands of Catla catla in- C111ACZ€d Spawning in Cirrhina reba, Barbus sarana and Cirrhina .n11r:i.gala, while glands of Labeo rohita induced successful SPIDZi‘Nning in Labeo rohita, Cirrhina reba and Barbus sarana 21:1(3 ovulation in Catla catla and Labeo bata. The results of experiments of the Indian workers may ‘363 zipplied in Pakistan as the carps are Similar in both the Countries. If successful, this may, in due course, lead to .tIIEE gproduction of quality stocking material on a commercial S‘:Eil_eu However, it is a fact that fish farmers are not well— (Diff- zand have no capital to invest, so stocking material must IDS: Blade available to them as cheaply as possible. Some time \Nfiill- be required to develop skill and avenues of supply for Stocking material from pituitary—treated Species. Hence it :LES ianortant to improve the Spawning grounds and encouraging E)()r“3- breeding to increase the supply and quality of stocking material. 94 The improvement of Spawning grounds is the concern of inland fisheries department and requires extensive re- search while pond breeding is the concern of the fish cul— turists. It has been found experimentally (Hora, 1945a) that carps do Spawn in Special "bundhs" or large embanked ponds where riverine conditions are Simulated. Further research in these lines is also needed. E. Procurement of Stocking Materials 1. Collection and Hatching of Carp Eggs in East Pakistan a. Collection.—-The professional fishermen collect the fertilized eggs within 14 hours of the Spawn from a 16 km. (lO—mile) zig-zag course of River Halda in Chittagong extending from Napitarghat to Ramdas Munshirhat (Ahmad, 1948). AS breeding grounds are situated very near the tidal zone, the eggs are collected shortly after Spawning, otherwise they are destroyed by the tidal brackish-water. The Spawning occurs during the full moon in the months of April to July (Ahmad, 1948). There may be as many as four Spawnings in one year. In the beginning of the Sea— son, the Spawn collectors fix their nets at suitable spots in the river and examine them carefully. As soon as some eggs are spotted, the collection is intensified. The collecting gear consists of a rectangular, 12 m. x 2.7 m. (39.4 ft. x 8.9 ft.) mosquito netting. It is 95 strengthened with ropes at the margins and ends are tied to two bamboo poles, each about 2.5 m. long. It is generally held from a boat by two men, one sitting at the bow and the other at the stern. The bamboo poles are fixed by means of wooden hooks to the sides of the boat. The net is lowered into the water in such a way that it remains behind the boat and does not get entangled. Some collectors stand knee to shoulder deep in the water with net. The eggs collect in a bag-like hollow of net formed by the force of the current. The net is hauled up when a Sufficient quantity of eggs are obtained. The collected eggs in various stages of develOpment are transferred to the boat, a part of which is partitioned breadthwize with mud. .Many eggs hatch here. Some loss of eggs takes place here due to congestion and lack of aeration. b. Hatching.--The eggs are transferred to hatching pits locally called ”hapas,” dug along muddy banks of the river and its tributaries within 4-5 hours of collection. The average size of hapa is 5 m. x 2.5 m.x 0.5 m. (16.4 ft. x 8.2 ft. x 1.6 ft.). The hapas are arranged in one or two rows, the one adjacent to the river gets its water supply direct from it through bamboo pipes or hollow betel nut trunks and the other row is fed from the first. The water is drained from the hapas into the river. The hapas are covered by a mosquito netting with its marginal ropes being tied to the wooden pegs on the ground at short distances. 96 The net is allowed to sag about 15 cm. (0.5 ft.) below the surface of the water in the Shape of a bag under which some strong bamboos are placed parallel to each other. These are frequently rolled with care in order to agitate the eggs to surface. Each hapa can accommodate 120 to 300 kg. of eggs numbering from 900,000 to 2.2 million. Taking 5 mm. as the average diameter of an egg, about 450,000 eggs can be Spread in a single layer in a hapa. The eggs hatch within 6—24 hours depending upon the stage of development of the eggs when they are introduced into the hapa and pass through the meshes of the nets into the water below. The net contains membranes of hatched eggs, dead and decomposed eggs, dead and live insect larvae, shrimps, etc. TheSe are removed along the net when all the larvae have hatched out. Carp larvae remain in the hapa for two days when they are col- 1ected with the help of close-woven sheets of cloth and transferred into another hapa containing fresh—water. This process is repeated for about a week. .The over-crowding of eggs in the mosquito netting and the consequent failure of many of them to hatch is one of the main reasons for low survival of eggs in the hapa. The provision of a rectangular tank-like structure made of net and the outer one of cloth has been suggested by Ahmad (1948). The corner of inner tank should be tied to the correSponding corners of the outer tank and the whole device is tied to bamboo poles. Thus as both the receptacles are 97 kept stretched, the eggs can be separated uniformly. The eggs should be introduced into the inner receptacle so that the hatched eggs passing through the meshes of the net into the cloth receptacle below can be removed easily. If a con~ stant flow of water is maintained, there will be no need to transfer the larvae from one hapa to another as is now prac— ticed. It is also suggested that instead of placing the eggs in the earthen enclosures in the boats where the water turns muddy and hampers the development of eggs, earthen vessels should be used. 2. Collection of Cagp Spawn The term "Spawn” applies to laid eggs with some hatchlings associated with them, but traders loosely apply it to cover eggs ("dim"),yolked larvae (”dimpona"), and fry up to 8 cm. long (”dhanipona”). "Phuldhani" is the name of fine dhanipona. Besides Chittagong, where only the eggs are collected carp fry are collected from the left bank of the Padma (or the Ganges) covering a distance of about 96 km. (60 miles) from Godagari Ghat to Sarda and small pockets of the Jamuna near Serajganj and the Padma near Raita. Generally speaking, the fry are collected from nearly all the rivers during the monsoon. The Spawn collection centers are selected on the basis of the empirical knowledge of the fishermen. The col- lection centers may change from year to year according to 98 the then prevailing topographical conditions. The collecting gear consists of a funnel-shaped net called "benchi jal.” The Spawn drifting down the river are caught within the wings and mouth of the net and led into a part of it called "gamcha" or rough cloth where they accumu- late. Usually 15 to 25 nets are operated by a group of 7 to 12 persons. The Spawn are removed hourly from the gamcha with the help of small bowls and allowed to pass through a crude Sieve to remove miscellaneous floating objects, debris, young Shrimps, fry of catfishes, etc. The catch from one benchi jal averages about 35,000 larvae. The sieved Spawn are placed in large earthen jars in the boat from which they are transferred to hapas for holding till distribution. Most of the Spawn develop into fry in the hapa. 3. Breeding the Major Carps in Bundhs Even though the eggs and fry of major carps are col- lected from rivers, some are also raised from Specially con- structed Spawning ponds called bundhs. These are small reservoirs actually meant for collecting and storing rain water. They are built in natural depressions, valleys or low lying rice fields in which rain water accumulates. The low end of such a depression is Surrounded on three sides by strong embankments. The bed of the reservoir is plain, a Shallow corner of which forms the Spawning ground called 99 moan. Some grass is grown on the moan to hold the soil and prevent the water from becoming muddy during collection of eggs. During the monsoon, rain water flows into the bundhs in streams locally called dhals. In Chittagong, a mud wall is raised in the upland area to hold the water which later flows into the bundh through a Slit made in the wall. An outlet is provided on the opposite Side of the bundh to drain off the used water. The bundh is stocked with breeders of the major carps (Catla catla, Labeo rohita, Cirrhina mrigala and Labeo calbasu) in the proportion of one female to two males as soon as the monsoon is set. In a bundh with the embankment of about 350 m. length, having a Spawning ground about 6,000 Sq. meters in area, 200 catla, 100 rohu, 100 mrigal and 40 kalbaus are stocked. When the water level in the bundh increases and shallow Spawning grounds are sub- merged,the brood fish gather there and start sex play. MaXimUm Spawning takes place at night during the full moon. The eggs are collected by using rectangular mosquito nets of 4 m. x 1.5 m. Size. Many eggs are destroyed by the Collectors trampling on them. The collected eggs are trans- ferred to earthen jars or kerosene tins and then to the hatching pits or hapas, Rows of hapas, each having the size 0 . f 1.3 m. length, 0.6 m. Width, and 0.3 m. depth are con— tructed in rice fields near the bundh. They are fed With 1: he Water overflowing the bundh through small canals. Six b . raSs bowls of eggs are released into each hapa filled with 100 water. The inlet is then closed and the temperature of the water rises thus reducing the hatching time, and within 24 hours the hatching operations are completed. Many eggs die in the stagnant waters of the hapa from bacterial action and lack of Sufficient aeration. The larvae are sold to nursery men and those left over are reared by the bundh owner in fry ponds. 4. Identification of Fry The carp fry are collected along with those of var- ious undesirable Species. Pond owners and fry collectors cannot differentiate between the fry of different carps below a size of 3 cm. Mookerjee et a1. (1944) and Alikunhi (1956) attempted to prepare a key to their identification (Table 15). F ° EanSport of Fish Fry 1 ‘ E‘Xisting Methods and Their Improvements Live fish fry are tranSported from the Spawning Sites to the nursing, rearing and stocking ponds which are S‘1131lated throughout East Pakistan, and in the Punjab and S ' . . 1nd Of West Pakistan (Figure 2). The fry are transferred by dipnet or by bucket into e arthen jars (”hundies"), each having a capacity of nearly 4 . O llters. A hundy contains about 60,000 larvae or fry 4-5 In In Generally, 75-100 g. of colloidal red soil - in length . i . S Stirred into each jar (this is, however, not practiced in 101 CDABLE 15. Salient characters of fry and fingerling of major carpsa 1.. Head conSpicuously large from 11.2 mm. stage and broad from 17.8 mm. stage. No barbels. Reddish color of gills visible through tranSparent Opercular flaps ' Catla catla LII. jHead of normal Size and shape. .AH Three to four black Spots on caudal peduncle enclos— ing a white Space. Lips fringed,-color generally grayish; a yellow spot at the anterior base of dor- sal fin and a yellowish band at the base. Barbels black . . . . . . . . . . . . . . . . Labeo calbasu E3. Spots on caudal peduncle not enclosing a white area. 1. Lips fringed. a. Body marked with longitudinal bands, with fine black dots . . . . Labeo gpnius b. Body without longitudinal bands, fins marked with vermillion red . ._. . . :Labeo rohita 2. Lips entire. a. Black Spot on either side of body on the 5th and 6th scales of the row above lateral line . . . . . . . . Labeo bata b. Black Spot abSent. 1) A black blotch at base of dorsal fin present . . . Barbus chola 2) Black blotch at base of dorsal fin absent. a) A Short, slanting vertical band later becoming an oval or round Spot below anterior end of dorsal fin . Barbus sarana c. Band or Spot below anterior end of dorsal fin absent. 1) Margin of lips black; minute black dots along lateral line at 11.5 mm. stage, later forming a longitudinal band . . . Cirrhina reba 2) ~Margin of lips rather whitish; body marked with several longitudinal black bands . . . . . . -,- Cirrhina mrigala aSourcesfi‘Mookerjee et al. (1944); Alikunhi (1956). 102 Chittagong, East Pakistan). The jars are carried to the nearest railroad station, slung on bamboo poles. During tranSport, the water in the jars is kept in constant agita- tion by the fishermen. This facilitates the elimination of accumulated CO2 and absorption of 02‘ Water is also changed from time to time. They may be tranSported to a distance of 100 miles or more for sale. The red soil used by the fry traders has a pH of about 8.5,Basu (1951) showed experimentally that this red clay helps in collecting dead larvae at the bottom. It is colloidal in nature and possesses a positive charge so that negatively charged dead and floating larvae attract the Clay, become heavy and Sink to the bottom and are removed. The dead ones get buried under the Soil that settles over them and organic pollution in the jars is thus localized to the bottom sludge. Saha and Chaudhury (1956), however, ob— Served that this soil has no eSpecial effect on the life of the fry; any ordinary soil in finely pulverized condition is as effective as the red soil in increasing the survival peri- od 0f the fry. Even though the jars are comparatively cheap and help in keeping the water cool during tranSport, their dis- advantage is that they are brittle. When fry transport is i . . . nteIlcled commerCially over long distances earthen jars are V . . er)! inconvenient to handle. 103 In order to prevent breakage of jars in transit and 'to change the water easily, fish transport cans (0.5 m. dia- meter at base and 38 cm. in height), as are used in Germany (Sch'aperclaus, 1933), may be tried in Pakistan. The can is fixed on a wooden base which avoids heating through contact with warm surfaces during tranSport. A close-fitting moist woolen jacket helps to maintain a uniform cool temperature during tranSport even when the can is exposed to the sun. Its mouth is about 20 cm. wide and has a pressed—in perfo— rated lid to admit air and at the same time prevents the Splashing of water or the fish from jumping out. Fifty to hundred fry can be tranSported in this type of tin can. See also Krause (1957), and Fry and Norris (1962) for further dEtails regarding the transport of fish in open containers. When tranSporting the fry by air, open containers Cannot be used. Hermetically sealed containers like air- tight tins used in tranSporting kerosene and gasoline with These containers have eXcess of 02 may be used (V335, 1952)- Wide mouths with a tightly fitting screw stOpper and washer. They have two metal pipes or rubber tubes, reaching the bot- tom, one with a narrow bore so that 02 can bubble through it. First , the container is filled to more than two-thirds with Clean, filtered pond water. Then the fry are introduced 1: . . . . hrough the mouth and the container is filled With water com— pletely to exclude all air. The mouth of the container is I) . 0‘” Closed and the O2 is introduced through the narrow pipe 104 from the oxygen cylinder through a regulator. Since the can is filled with water, a volume of water equal to the volume of oxygen introduced will be diSplaced through the second By measuring this volume, it can be ascertained wheth— When pipe. er the required quantity of oxygen has been introduced. sufficient oxygen has been introduced, both the pipes are hermetically sealed (Vaas, 1952). Plastic—bag tranSport (Miller, 1956) of live fish first came into general use less than a decade ago. The usual method of using plastic bags for shipping is to place two bags, one inside the other, in a cardboard box. This bOX is often insulated with Slabs of glass wool or expanded cardboard. The desired amount of water, usually 5 gallons Or less, is poured into the inner bag. The fish are intro— duced and the bag is partially inflated with oxygen and Sealed with rubber bands. The box is then sealed and Shipped to its destination by air. The primary advantages of the method are reduction in Shipping weight and reduction of injury resulting from fish hitting container walls (Fry and Norris , 1962) . In closed containers CO2 will necessarily build up 1n the water. Acid pH caused by CO‘2 may be counteracted by 1: - . r15 (hydroxymethyl) aminomethane, an organic buffer, which S . hoWed a 50-fold increase in buffering capacity at 20 g. per gallon with maximum hydrogen ion absorption between a pH of ’7 ‘5 and 8.5 (McFarland and Norris, 1958). Inorganic buffers 105 like boric acid, sodium monophOSphate, sodium biphosphate and sodium bicarbonate have been tested with conflicting results (Vaas, 1952; Srinivasan et al., 1956). Ammonia will largely be neutralized by the reSpiratory C02. See also Alabaster and Herbert (1954). The problems which must be met in the successful transportation of live fish fry are many and diverse. The primary problem arises from the low capacity of water for oxygen together with its low capability to dissipate the end products of metabolism. The second problem is that of han- dling. In delicate Species, abrasion needs only to be suf- ficient to remove the mucus from a fraction of the area of the skin in order to rob them of essential protection from Osmotic stress. Many fish, too, are so stimulated by han- dling that they readily accumulate dangerous levels of lac- tic acid in their blood (Black, 1958). Excessive changes in temperature are also deleterious, as is well known. For a recient review on these crucial factors see Norris et al. C 1960). The optimum number or weight of different Species of fry or larvae that can be tranSported in a container, open .Qr Closed, depends upon the species (rate of reSpiration), 15h size, general physiological and health condition of the f ‘ . 15h: the water temperature in the tranSporting vessel, and 't he Cluration of the transport (Krause, 1957). .Hora and P . lllay (1962) write that tins of 18 liter capacity are used 106 in India to transport the fry of major carps in presence of 6 liters of free oxygen. In such tins, 900 to 1,000 fry of 1-2 cm. length or about 285 g. of fry of that length can safely be tranSported by air for over 20 hours. They (1962) have quoted the following figures (Table 16) from the Hong Kong Fisheries Research Station regarding the tranSport of such Chinese carps as grass carp (Ctenopharyngodon idellus), big head (Aristichthys nobilis), silver carp (HypOphthal- michthys molitrix), and common carp (Cyprinus carpio). These data may be useful as a guide in fry transport in Pakistan. 2. Ellysiological Requirements Jspiration-—The Level The level of oxygen required is something more than the bare minimum that will prevent aSphyxia in an undisturbed fish. Fish must at least perform compensatory movements throughout the journey. Furthermore, fish are easily Stim- Ulated to increase their oxygen consumption to near their Imaximum rates, and are slow to return to the resting level, so 1:hat the excitement of capture and transfer to the trans— p03fting containers is likely to increase greatly the need for Oxygen. There is also the possibility that an initial severe Struggle may lessen the ability of the blood to transport QXVSEn for some time afterward. A suitable physiological Stallciard for the oxygen consumption of fish fry in tranSport 107 TABLE 16. Number of Chinese carp fry that can be tranSported in a container of 18.5 liter capacity containing 8.5 liters of free oxygena ESize of Weight per Number of Amount of fry 1,000 fry fry free oxygen per g. of fry (mm) (g) (ml) LID—20 50-200 4,000-5,000 42.5 30 450 1,500—2,000 12.9 40 800 800-2,000 10.6 50 1,500 500- 800 5.7 00 2,500 400— 500 3.4 70 3,000 350— 400 2.8 80 3,500 250- 300 2.4 90 4,500 200 1.9 100 6,000 150 1.4 110 8,000 100 0.85 120 12,000 80 0.70 \ aSource: Hora and Pillay (1962). 108 is 50% more than they require strictly for maintenance in an undisturbed state (Fry, 1957). Large individuals consume less oxygen per unit weight as is well known. The consumption of than do the small ones, oxygen rises with temperature up to an Optimum level but is relatively independent of size (Job, 1955). The metabolic rate rises proportionately up to an optimum temperature (:290C in case of milkfish) and then falls (Job, 1957). The rtelative increase in rate of oxygen consumption is greatest iii fish fry. Saha et al. (1956a) found that the fry of major (zzirps cannot live in oxygen concentration below 0.5 p.p.m. I=JTy which are 4-8 cm. long can stand oxygen concentration up 1rc> 25 p.p.m. in the water for over 24 hours. For every milliliter of oxygen that a fish consumes, ‘iTEI will produce approximately 0.9 ml. of carbon dioxide. jrldxs fate of this gas will be to enter into the equilibrium ESEVStem of carbonates, bicarbonates and free carbon dioxide Ci-‘i.:ssolved in the water. From the point of view of reSpira- t:3iJDn, only the fraction that accumulates as free carbon diox- ii‘:l€3 needs to be considered. The effect of increase in free CEi-rbon dioxide is to depress the ability to take up oxygen ( Basu, 1959). When oxygen concentration was 2 p.p.m. or , carbon dioxide was found lethal for the fry of major (333.1jps at 250 p.p.m. (Saha et al., 1956a). 109 Accumulation of Ammonia Nearly 50% of the nitrogenous excretion of fish is ammonia which, in non—ionic free form, is a toxic substance (Duodoroff and Katz, 1950). Saha et al. (1956b), however, have found that the fry of major carps can tolerate 20 p.p.m. of dissolved free ammonia and 15 p.p.m. of ammonia in the .form of inorganic salts. 13- Conditioning Fry that are transported immediately after collection Ilzive low Survival rate as they are suddenly kept congested Lira containers where they vomit the food eaten before capture To ()1? pass excreta which aggravates the oxygen demand. aVOid this, fish farmers in East Pakistan condition the fry t3)? keeping them in small nursery ponds for 12—24 hours after Here they clean themselves and get accustomed C Ollection . t3<> living in limited Space with comparatively less oxygen C Ahmad, 1957a). C; - Nursing and Rearing Carp Spawn JL - Principles In East Pakistan, Before considering pond culture or stock— ponds, lakes, and reservoirs are LlS€3d for stocking. ing operations (see page 113), it will not be out of place to (2‘3’rlsider nursing and rearing the carp Spawn near the collec— 1b4i—<311 site before, or the stocking sites after, transport. 110 Although a stocking pond is much safer for the young fish than the natural waters, it is not recommended that they should be released there right after collection or Their food and feeding habits are, in many transport. Little care can cases, different from those of the adults. possibly by given to the young fish if they are released in 'the stocking ponds where associations of different size- ggroups or Species are raised. They will be exposed to pre- ciation and their numbers greatly reduced. In view of these c<3nsiderations, it is important to rear the young up to the .fUingerling stage in separate nursing and rearing ponds be- 17c3re transferring them to the stocking ponds. Nursing ponds should be less than one—third of an Elczre in size, while the rearing ponds may be larger than tillaig The small size of nursing and rearing ponds facil— i“Crates efficient control of ecological conditions such as tiller quality and quantity of water, condition of soil, pre— C1-'=3.‘I:ion, etc. These ponds should be less than three feet 'j—Il depth, as the fry need warm waters for rapid growth. Besides, shallow waters promote growth of their food such ‘8‘53 blue-green algae and diatoms. Other advantages of shallow nursing and rearing I)‘l‘Jr‘ids are as follows: (a) they are easily drainable; (b) ‘t:1113y dry up during later winter months and their bottom muds 23‘17EE aerated and mineralized, production of H25 is interrupted Ellj‘j- oxidation of organic matter initiated; (c) the fish 111 enemies living in the ponds can be controlled; (d) applica- tion of poisons to control predators resistant to drying or of manures to increase their productivity is easier; (e) cultivation of leguminous plants to increase productivity of the bottom soil by fixing atmOSpheric nitrogen is pos- sible; (f) harvesting of fry will be easy; and (g) large stocks of fry can be raised in close proximity to the areas selected for fish farming (Hora, 1945b). 2. Procedures a. The seasonal ponds to be used as nurseries should first of all be drained to dryness. b. The thoroughly dried bottom of the pond should be ploughed well and short-season crops like legumes grown to increase productivity of the bottom. It should again be ploughed and leveled when the crop is harvested. If the pond soil is acidic, liming should be done so as to bring the pH up to 8.5. c. Manuring of nursery ponds may be done with cow-dung at the rate of 250 kg. (550 pounds) per hectare. d. Ponds are filled with rain or any clean water from a nearby source. e. Eradication of predators is possible in a drainable pond. If a perennial pond is used as a nursery, predatory fishes and insects may be eradicated by applying rotenone evenly at the rate of 4-6 p.p.m. on a quiet day. The 112 dead or stunned predators should be removed from the pond and destroyed. Measures such as Spraying of an emulsion of 56 kg. of mustard oil and 19 kg. of washing soap per hectare of pond surface will remove predatory insects (Hora, 1945b). Access of external predators to the nursing ponds may be checked by fencing the embank- ments. At least three million fry can be reared to fingerlings in 15 days in a nursery pond having an area of 0.5 hec- tare. The plankton produced by manuring with cow—dung are generally zooplankters which are excellent food for the carp fry. If there is any chance of pollution, the plankton may be raised in small ditches and transferred to the nursing pond. In case of waterbloom, duckweeds (Lemna Sp.) may be released in these ponds which will cut off light penetration and the bloom will die out. If the natural food is insufficient in a nursery, re— peated transplantations and artificial food will enhance their growth. Fry fed on oil cakes at the rate of one to three times the weight of the fry at the time of re- leasing into the nursery grow rapidly. Hora and Pillay (1962) suggested the following feeding schedule: 1) First five days after stocking: Artificial food equal in weight to that of the fry stocked. 113 2) Second period of five days after stocking: Twice the weight of fry at the time of stocking. 3) Third period of five days after stocking: Three times the weight of fry at the time of stocking, A fry about 6 mm. long weighs nearly 0.0014 g. and a bowl 7.6 cm. in diameter and 3.2 cm. in width holds about 30,000 fry of the said length. For each bowl of fry, 4 bowls of rice bran, 3 bowls of mustard oil cake, and 2.5 bowls of peanut oil cake are the estimated feed. h. After 15 days the fry which are now about 35 mm. long should be removed to rearing ponds. The fry collecting net may have a mesh size of 13 mm. A nursery pond can be used to rear successive lots of fry. The preparation and management of rearing ponds are similar to those of the nursing ponds. Fry of about 35 mm. length should be stocked in rearing ponds at the rate of 250,000 to 500,000 per hectare of pond area. When they grow up to fingerling stage (l30~155 mm.), they are safe for transfer to stocking ponds. H. Fish Culture in Freshwater Ponds Fish culture in Pakistan can be divided into the following categories: a. Fish culture in fresh-water ponds b. Fish culture in lakes, reservoirs, swamps and irrigation canals 114 c. Fish in rice fields d. Fish culture in brackish-water swamps and rice fields. These will now be considered separately. 1. ,The Pond a. Definition A pond is a body of water having slight depth occupy— ing a basin and lacking continuity with the sea (Forel, 1892). It does not stratify thermally (Muttkowski, 1918). It is a quiet body of water in which the littoral zone of floating- leaved vegetation may extend to the middle of the basin and in which the biota is very similar to that of the littoral zone of lakes (Welch, 1952). In pond industry, the fish pond always signifies a drainable flat body of water (Schaperclaus, 1933). Pond culture is profitable only under favorable fishing condi- tions, i.e., where drainage of ponds or fishing with nets is possible. Non—drainable ponds with the exception of drink- ing water ponds and village ponds are less productive than the drainable ones. Thus the ponds are: (l) non—drainable, (2) drainable or true fish ponds. In reSpect of water supply, ponds are: (1) Spring water ponds (mostly in West Pakistan); (2) rain water ponds (in East Pakistan); (3) brook ponds such as feeder ponds; or (4) river ponds. 115 According to origin, ponds are those (1) which rep- resent the pond stage in the extinction of previously exist- ing lakes; (2) which have not been preceded by a lake; and (3) those which are the results of man's activities (excava- tions, quarries, etc.). It is the third category of ponds on which the following discussion will largely be based. b. Fish Ponds of East Pakistan Fresh—water ponds are a distinct element in the village economy of this province. In addition to innumer- able water—filled ditches, this province has 264,355 ponds (Table 17), 150,000 of which are regularly stocked with fish (Ahmad, 1957c). Village ponds are used for bathing, washing, and watering livestock. They are the communal property of the village. Homestead ponds are more numerous in the southern districts of the province (Figure 7). Here borrow-pits have to be dug in almost every home for construction of houses and reclamation of low—lying areas. Homestead ponds are used for the supply of drinking water as well as fish culture. Little attention is being given to the upkeep of these ponds. They may be overgrown with vegetation except at the Spots used for domestic purposes, and form permanent breeding areas for mosquitoes. 116 a TABLE 17. Distribution of ponds in East Pakistan Name of Districts Number of ponds Noakhali . . . . . . . . . . . . . . . . . 43,747 Faridpur . . . . . . . . . . . . . . . . . 38,517 Mymensingh . . . . . . . . . . . . . . . . 26,845 Comilla . . . . . . . . . . . . . . . . . 26,230 Dacca . . . . . . . . . . . . . . . . . . 19,394 Khulna . . . . . . . . . . . . . . . . . . 17,649 Bogra . . . . . . . . . . . . . . . . . . 16,988 Rajshahi . . . . . . . . . . . . . . . . . 16,179 Dinajpur . . . . . . . . . . . . . . . . . 15,109 Jessore . . . . . . . . . . . . . . . . . 14,274 Barisal . . . . . . . . . . . . . . . . . 7,288 Chittagong . . . . . . . . . . . . . . . . 6,985 Rangpur . . . . . . . . . . . . . . . . . 5,016 Sylhet . . . . . . . . . . . . . . . . . . 4,699 Kushtia . . . . . . . . . . . . . . . . . 3,330 Pubna . . . . . . . . . . . . . . . . . . 1,805 Chittagong Hill Tracts . . . . . . . . . . 200 Total . . . . . . . . . . 264,355 Area of East Pakistan . . . 54,501 sq. mi. (14.1 mill. ha.) ,Area of ponds . . . . . . . . . . . 75,000 ha. % of area of ponds to total area of the province . . . . . . . . . . . . . . . . 0.5 3Source: Ahmad (1957c). 117 c. Improvement of Existing Ponds To increase the production of fish in ponds, the immediate need is to improve the present ones rather than constructing expensive new ones. In order to improve these ponds, 1) 2) 3) 4) 5) it is essential to: Control growth of aquatic plants in such a way as to discourage quick regrowth. Measures of their control will be dealt with on page 146. Drain and desilt them. Draining will be easy when ponds are situated in areas where the water can be drained off into other low-lying areas. Otherwise expensive mechanical devices will be required. The silt removed from the pond can be uSed to repair embankments, or it may be used in gardens and agri— cultural lands. If it cannot be drained because of depth or restricted water supply, some of the exces— sive organic deposits may be removed by using flat bamboo shovels fitted with long handles in order to reach the pond bottom. The deposit is collected and placed in boats or thrown to the banks. Remove the predators by repeated fishing or by suit— able poison. Raise and strengthen the embankments, wherever neces- sary. Provide each pond with an inlet and an outlet. These may be of wood because concrete and galvanized iron 118 pipes will be costly. The inlet and outlet should be provided with fine—meshed sieves to prevent the extraneous and predatory fish from entering the pond and stopping the escape of those being cultured in it. d. Construction of Fishponds Ponds meant for fish culture need special construc- tion. It is the most expensive part of the whole enterprise and success or failure of it depends, to a large extent, on the suitability of the pond constructed. Pond construction is an engineering problem. Insufficient training in this field is likely to lead to the selection of unsuitable Site, and faulty construction, resulting in the loss of money and effort. Topography of the area, nature of soil, water supply, etc. should be considered in detail before the actual con- struction work is started. Selection of site.——When making a choice for the 10- cation of a pond, it is necessary to consider that a location upon a muddy or clayey soil is profitable because such soil is otherwise unusable. If a pond is at all constructed on a potential agricultural land, it does not necessarily compete with its agricultural use as it is also used for other pur- poses like growing water chestnut and water lily for human consumption and sometimes water hyacinth for cattle. Duck raising is also carried on concurrently (Hickling, 1948). 119 Low—lying areas of the districts of Noakhali, Faridpur, Mymensingh, Comilla, Dacca, Barisal, Khulna and Sylhet are ideal for pond construction (Figure 7). Easy approachability is an important factor in site selection. In deltaic regions, and areas adjoining rivers, canals and lakes, water transport will be possible and this will reduce the cost of the supply of stocking material as well as mar— keting the produce. The problem of water—logging which is looming large in part of West Pakistan can be solved to some extent by fish culture. For this purpose, the water pumped out of the boggy land may be collected in ponds dug-out at the lowest level of the land, water weeds and hydrophytes planted there— in and fish introduced. The returns from the sale of fish will meet to a great extent the cost of pumping and digging the ponds. The water will be free of salts after some time as the vegetation will absorb the salts. Euryhaline fishes like Tilapia, will be ideal for culture in such waters. Water supply.——Although ponds are fed with rain water, it is desirable to have them constructed in areas where running water is always available because draught or untimely rainfall may be a hindrance to fish culture. For all types of ponds, the availability of water from river, canal, tube well, artesian well or Spring is desirable. Hickling (1962) has shown that, for a pond of one acre, three feet deep, about 816,750 gallons of water will be 120 Figure 7. Map of East Pakistan showing the districts, the Sunddrbans and the major fresh—water rivers. 121 - ‘1 EAST PAKISTAN SYLHET BAY OF BENGAL Figure 7 122 needed to fill, and, aSSuming a rate of loss through seepage and evaporation of half—inch per day or three and a half inches per week, about 80,000 gallons per week are needed to keep it filled. This is a moderate amount of water, equivalent to three and a half hours' inflow at one cubic foot per second. The site should be free from flooding and surface drainage, as these might cause washout of the dykes resulting in loss of fish. Size and shape.——The usual size of a pond is one- third to three acres. It may be of any shape, but a rectan- gular pond is desirable, as it will facilitate the removal of fish by nets Operated from one end of the pond to the other. The depth of a fish pond ranges from l—2.5 m. The pond site should first of all be cleared of all trees, brush, etc. The top soil is collected and kept aside for use as fertilizer. The surface soil is kept for fencing the embankments on which grass and other vegetation are grown. The shape of the embankment depends on the type of soil, but generally a slope of 3:1 is considered adequate (Hora and Pillay, 1962). Inlet and outlet arrangements.——The inlet is pro— vided near the source of water supply and outlet at the deepest portion of the pond. The inlet should be guarded against the entrance of undesirable fishes by means of fine— meshed screens. Hollow palm or betelnut stem is generally used as inlet pipe. 123 Prevention of seepage.--New1y constructed ponds do not usually hold sufficient water if they are situated on gravelly or sandy soil. The bottom of such ponds should be covered with a layer of mud or clay at least 20 cm. thick before they are filled. This will reduce considerably the loss of water due to seepage. Other arrangements.--The whole fish pond should have a good fencing to prevent the entry of cattle, etc. A few shade trees may be grown near some portions of the pond to give shade where the fish may protect themselves from the heat of the summer sun. In shallow ponds, marginal and cen— tral ditches may be dug where the fish may retreat during hot days. 2. The Water Two fundamentally different requirements confront the fish culturist with regard to the physical and chemical conditions of water which is the basic element in fish cul- ture. They are: (l) The water must offer the fish (as well as other biologically productive organisms) near optimum physical conditions of existence. (2) The water must con- tain the nutrients needed for primary production in optimal amounts, or they must be regularly renewed from outside or must be replenished through the process of decomposition within the pond. These two requirements are physico—chemical in nature and overlap each other. 124 a. Physical Properties of Pond Water Shallowness.——The relatively high productivity of the pond is, to a large extent, due to its shallowness which allows the penetration of light to its very bottom, and at the same time facilitates the rapid warming process of the water mass. The strata below two meters add little biolog— ical production in tropical regions. However, ponds shal- lower than one meter may develop temperatures high enough to affect productivity adversely and may lead to loss of fish. In a shallow pond, soil and water have greater sur- face of contact per unit of volume than a deep pond, so that more nutritional matter from the soil is dissolved which usually means greater productivity. ‘Light.—-The shallow depths of ponds usually make possible an illumination of the entire bottom by effective light so that plants may occupy the entire basin. Luxuriant growth of plants produce, of course, much shading of the underlying waters. Unshaded ponds with clear water may be illuminated through with an intensity almost as great as that of the surface. Light penetration is much affected by the irregular and sometimes abrupt variation in turbidity. Since the shallowness allows such complete illumination it follows that ponds, in general, are subject to the range of the daily seasonal variations in light supply. Solar heat.—— Solar heat keeps the surface tempera- ture of ponds constantly high thereby creating a stratifica— tion in them. Three distinct water layers are recognized: 125 (l) the epilimnion or the warmer waters of the surface zone, (2) the thermocline, a thin middle layer where the tempera— ture drops abruptly, and (3) the hypolimnion, or the cooler water at the bottom. This thermal stratification may not be prominent in shallow ponds. It is generally believed that the surface layer of water in tropical climates does not mix completely with the layer below three meters except in ponds exposed to strong wind action. Instead of an annual turn-over, as found in temperate climates, a daily turn- over takes place in trOpical ponds at night bringing about a mixing of the water. This turn—over is of extreme impor- tance in the circulation of oxygen and nutrients in pond water (Hora and Pillay, 1962). Temperature.-—The temperature of water is obviously very important. All activities of poikilothermous creatures slow down as the temperature falls. Carp stops feeding at 10°C and becomes torpid at about 50C (Hickling, 1962). Probst (1950) has shown that the yield of carp ponds is positively correlated with average temperature during the growing period (May to September). In Pakistan, there is little seasonal variation in temperature which is also high (Table 3), fish growth may proceed the year round, so that it is possible for fish ponds to show very high productivity. Because of shallow depth and large expanse of surface as compared with the volume, pond waters, in general, tend to follow the temperature of the atmOSphere. A rise in 126 temperature causes downward migration of surface biota. High temperatures decrease the dissolved oxygen content of the water, increases oxygen consumption of the biota and the mineralization of organic matter. The temperature tolerance of various fishes cultured in Pakistan has so far not been explored. Turbidity.--Turbidity, due either to plankton growths or to non—living suSpended matter, varies greatly with the circumstances of season, productivity, nature of the basin, degree of exposure, rains, floods, inflowing sediments and other similar features. In turbid water, the photosynthetic rate will be reduced and the fish fauna need- ing clear, oxygen—rich water will be replaced by a predom— inantly labyrinthiform fauna. The turbidity tolerance of various cultivated Species of fish is not yet known, al- though catfishes have been found well-suited for turbid waters. Water movement.--Owing to the small area involved, water movements in ponds are minimal. Even in the most ex- posed ponds, wave action is very slight. Luxuriant plant growth, often accompanying features of ponds, further re- stricts water movements. Water movement or a current of water is necessary for the breeding of carps, although most of Pakistan's cultivated fishes can grow and fatten in lentic environments. 127 b. Chemical Properties of Pond Water The existence and nutrition of the biologically active organisms in the pond depend upon the basic chemical elements, ten of which are of great importance: oxygen, hydrogen, carbon, nitrogen, sulfur, phOSphorus, potassium, calcium, magnesium, iron, and of minor importance are: sodium, chlorine, fluorine, silicon, manganese, iodine and arsenic. Most of these substances are found dissolved in the water in sufficient quantities through contact of the water with the soil and the air. Undissolved supplies come into the pond through inflow during rains and floods. The above-mentioned substances are present in the water in com— bined forms. They may be poisonous in free forms. They must be present in usable and combined forms since the qual— ity of the water depends on the nature of their available combinations. Dissolved oxygen.--Dissolved oxygen is important for the reSpiration of fish and other living organisms in the pond, with the exception of some anaerobic bacteria. It is obtained from the atmOSphere, and the aquatic plant photo— synthesis. The oxygen carrying capacity of the water varies with its temperature and an increase in temperature results in a decrease in oxygen solubility. The figures in Table 18 show the normals (Schaperclaus, 1933). 128 TABLE 18. Temperature and dissolved oxygen relationship in pond water3 Temperature .Oxygen (0C) (mg/liter or p.p.m.) O . . . . . . 14.57 5 . . . . . . 12.74 10 . . . . . . 11.25 15 . . . . . . 10.07 20 . . . . . . 9.10 25 . . . . . . 8.27 30 . . . . . . 7.25 aSource: Schaperclaus (1933). 129 While the dissolved oxygen content decreases with the increase in temperature, the oxygen consumption of fish in— creases with the increase in temperature. Absence of aquatic plants and putrefaction of organic matter cause diminution to depletion of dissolved oxygen. Wunder (1949) states that a dangerous oxygen deficiency may be caused in fish ponds as a result of fertilization. A very rich algal flora may develop which yields a high oxygen content to the water dur— ing the day, but at night the respiration of algae may re- duce it to dangerously low levels. There is a diurnal variation in the dissolved oxygen content of a pond; its quantity is least at dawn. Buschkiel (1937) shows that deoxygenation at night may be naturally prevented even where the pond is treated with large quanti- ties of organic manures. The oxygen bubbles present in the algae at daytime dissolve at night helping to keep the fish alive until oxygen production begins again at dawn. The rate of oxygen consumption of various cultivated Species of fish in their different ages is not yet determined. It is eStimated that a concentration of 5 p.p.m. at 200C or over is sufficient to keep the fish healthy, supersaturation of oxygen has little ill-effect on fish (Hora and Pillay, 1962). .Biochemical oxygen demand (B.O.D.).——Biochemical oxygen demand is the amount of oxygen used up during the oxidation of three classes of materials: (1) carbonaceous 130 organic material usable as source of food by aerobic organ- isms; (2) oxidizable nitrogen derived from nitrite, ammonia, and organic nitrogen compounds which serve as food for Specific bacteria (e.g., Nitrosomonas and Nitrobacter); and (3) certain chemical reducing compounds (ferrous iron, sul- fite, and sulfide) which will react with molecularly dis— solved oxygen. In raw and settled domestic sewage, most—— and for practical purposes, all—-of the oxygen demand is due to the first class of materials, while, in biologically treated effluents a considerable proportion of the oxygen may be due to oxidation of Class (2) compounds. The oxygen demand for Class (1) and (2) materials can be determined by a standard B.O.D. test but for Class (3) materials similar B.O.D. test may not be conducted unless it is based upon a calculated initial dissolved oxygen (American Public Health Association, 1962). It should be borne in mind that all three of these classes will have a direct bearing upon the oxygen balance of the receiving water and must be considered in the discharge of waste in such a water, because a rise in oxygen demand may mean depletion of oxygen and consequent death of fish. EH rate.--The natural reaction of any liquid, includ— ing pond water, may be either alkaline (pH greater than 7.0), acidic (pH less than 7.0) or neutral (pH equivalent to 7.0). A good pond water has a pH rate of from 7 to 8 which means a feeble alkaline reaction. Dissolved calcium bicarbonate is 131 mainly responsible for the maintenance of such an optimal range of pH. A good pond water having adequate acid com- bining capacity will not show a pH range higher than 6.5 to 9.0 (Schaperclaus, 1933; Swingle, 1957). Swingle states that waters more alkaline than 9.5 are unproductive because carbon dioxide becomes unavailable in such alkaline water-- the alkaline death point of fish being about 11.0. Many fish can tolerate wide ranges of pH. Swamp fishes like the snakeheads (Ophicephalus spp.) and some catfishes are known to live well in waters having a pH range of 4 to 9. Acid water may diminish the appetite of fish and so reduce the rate of their growth. Acid water is less pro— ductive because there is a lack of carbon dioxide for photo- synthesis. Alikunhi (1957) confirms that in India water on acid soil is generally less productive of fish than that on alkaline soil. In Madras State, India, waters of pH 6.5 to 7.5 gave an average yield of 200-500 pounds per acre, where- as, that of a pH 7.5 to 8.5 gave 1,000-2,000 pounds without feeding. Generally a pH lower than 5.0 is considered unsuit- able for fish life. Water with a pH of 4.0 cannot be used for fish culture. Those of pH 4.5 to 6.5 can be improved by sufficient liming to bring up the pH to about 8.0 (Schaperclaus, 1933). 132 Alkalinity reserve or bicarbonate buffering system.—- Alkalinity reserve is also known as acid combining capacity or titration alkalinity. It can be expressed as the calcium content of the water. It controls the extreme variation of pH. The process is like this: at an alkaline reserve of 7 c.c. N HCl per liter which corresponds to 196 mg. of CaO per liter (p.p.m.) the water contains 308 mg. per liter of calcium bicarbonate which again correSponds to 101.0 mg. of free CO per liter. This will correSpond to pH 7.0. If, 2 due to photosynthesis, it loses 1 mg. of free CO the pH 27 will rise due to loss of acid prOpertieS. A part of calcium bicarbonate dissolved in the water will break down into calcium carbonate and free CO2 until a free equilibrium and a correSponding pH is brought about. Calcium carbonate is deposited on the plants, or settled at the pond bottom. Con- versely, when the water contains free CO higher than 101.0 2 mg. per liter and the pH is consequently low (acidic), the excess of CO2 dissolves the CaCO3 deposited on the pond bottom into calcium bicarbonate (Ca(HCO ). The alkalinity 3)2 reserve increases bringing up the pH and establishing the necessary equilibrium. This is a reversible process which can be expressed in the following equation: C CO = C0 +CO+HO a(H 3)2 Ca 3 2 2 This process takes place in the pond continuously and ac- counts for the fluctuation in pH. 133 Schaperclaus (1933) gives a table (Table 19) in which the alkalinity of the water, as measured by a Simple and easy titration of the water, is correlated with its potential productivity of fish. According to Schfiperclaus, the most productive water is that which titrates 2—5 c.c. Hey (1947) observed that values between: O-O.15 c.c. N HCl/liter—-too acid to be of any value for fish culture 0.15-2.0 c.c. N HCl/liter-—usable but acid 3.5 c.c. N HCl/liter--optimum. Free COZ.-—Water contains free carbon dioxide either from the atmOSphere, or from the decomposition of organic matter and as a result of reSpiration of aquatic organisms. Accumulation of free CO2 takes place generally at night. High CO content prevents oxygenation of water and 2 may also adversely affect the extraction of dissolved oxygen from it by animals. Generally, 5 c.c. of CO2 per liter is the upper limit for healthy growth of fish (Hora and Pillay, 1962). C02 Tension.--Carbon dioxide tension is equal to the pressure or tension of CO2 in the air above after the equi— librium has been reached in the water. It is not a measure of the total CO2 present in the water but is a measure of its availability for photosynthetic purposes (Swingle, 1947). The actual amount of CO2 present as free CO and as 134 TABLE 19. Alkalinity and pond cultural significancea Alkalinity expressed as c.c. N/lO HCl required to neutralize 100 c.c. pond- water Pond cultural significance Zero or negative Water strongly acidic, unus- able for fish culture, liming unprofitable in most cases. 0.1-0.5 c.c., equivalent to 2-8 drops of N/lO HCl Alkalinity very low. Danger of fish dying, pH variable, CO supply poor, water not vegy productive. 0.5-2.0 c.c., equivalent to 8-30 drops of N/lO HCl pH variable, CO supply medium, productivity medium. 2.0-5.0 c.c., equivalent to 30-75 drops of N/lO HCl pH varies only between narrow limits, CO supply and productiviéy optimal. 5.0 c.c., equivalent to 75 drops of N/lO HCl Rarely found, pH very con— stant, productivity alleged to decline but not proven so far. Health of fish not en— dangered. aSource: Schaperclaus (1933). 135 bicarbonate CO2 at any given CO2 tension varies depending upon the concentration of salts and kind of salts in solu- tion and the temperature of the solution. The CO2 tension of the fish's blood and that of the water in which it lives both exert a powerful influence upon reSpiration. A high CO2 tension in the water would have the effect of reducing both the speed of oxygen absorption and the amount carried by the hemoglobin. Swingle (1947) con- cludes that a greater increase in CO2 tension of the water in order to increase algal production would eventually re- sult in death of fish by aSphyxiation, therefore, great care must be taken not to increase the tension too rapidly or too high. Nitrogen.-—Nitrogen is a necessary element in the productivity of a pond. It is obtained through the putrefac- tion cycle. The nitrogenous compounds in waste matter are broken down by the anaerobic bacteria into ammonia and other compounds. In the presence of oxygen, the aerobic bacteria oxidise ammonia into nitrites and nitrates. Nitrate nitrogen is available to the various forms of life in the pond. Again, the denitrifying bacteria break down nitrates eventually pro- ducing free nitrogen. The nitrogen cycle is very important in the life of the pond. Adequate quantities of nitrate nitrogen are essen- tial for its productivity (Pearsall, 1932). ,The best produc- tion of plankton is obtained when the water contains 4 p.p.m. 136 nitrogen along with l p.p.m. potassium. The healthy growth of fish can be expected in waters containing less than 2 p.p.m. dissolved ammonia. The toxic effect of ammonia compounds is at a maximum when pH ranges from 7.4 to 8.5 (Hora and Pillay, 1962). §z§.--Sulfurated hydrogen is a severe limiting fac- tor in fish ponds. It is formed during decay of organic matter. It accumulates in the pond bottom having a thick layer of organic deposits. A concentration of 6 p.p.m. of H25 can kill common carp within a few hours. Mechanical aeration of the pond helps reduce its H25 content. PhosphoruS.--PhOSphoruS is a crucial factor in the biogeochemical cycles. This importance stems from the fact that phOSphorus is vitally necessary in the operation of energy transfer systems of the cell and that it normally occurs in very small quantities. The latter factor means that there is a chance of deficiency of the nutrient which in turn could lead to inhibition of phytoplankton increase, resulting ultimately in decreased productivity in the pond or lake. PhOSphorus occurs in several forms but only soluble phOSphate phOSphorus and soluble organic phOSphorus are of importance in natural waters. In water, phOSphorus may enter into combination with a number of ions but more conspicuously perhaps with iron and with the usually abundant calcium. The pH of the water determines to a great extent the nature of 137 the phOSphate compound. In neutral and Slightly alkaline conditions, calcium phOSphate is probably prevalent, while extremely high pH usually results in the formation of sodium phosphate. In acid waters, phOSphate attraction swings to- ward iron to form ferric phOSphate. The concentration of total exchangeable phosphorus in natural waters is determined primarily by (1) basin morphometry, as it relates to volume and dilution and to stratification or water movements; (2) chemical composition of the geological formations of the area, as they contribute dissolved phOSphate; (3) drainage area features in relation to introduction of organic matter; and (4) organic metabolism within the body of water and the rate at which phOSphorus is lost to sediments. See further Pearsall (1932); and Hutchin— son (1957). Potassium.-—Potassium is another chemical element reSponsible for the productivity of a pond. Sandy soil is usually poor in it but clay soil is usually rich in it. It is important for the growth of aquatic flora. It is released into the water directly from the plant tissues when they de- compose. A concentration of l p.p.m. K in combination with l p.p.m. P and 4 p.p.m. N is believed to be most favorable for plankton production. 138 3. The Soil Fish culture can use soils of poor or marginal agri- cultural value such as undrainable marshlands, sandy and acid soils. Schaperclaus (1959) writes that the large and important fish farming in Lusatia, Germany, is situated on the poorest soils from the point of view of agriculture and forestry. De Bont (1952) reports that ponds constructed on lands valueless for other purposes in the Congo could pro- duce as much as 9,000 kg/ha/annum with feeding. It is, however, not suggested that only poor soil is good for fish culture but the basic requirements of fish culture are less exacting than in agriculture and that, fish culture can bring such unproductive lands into good use. Poor lands under fish culture can yield as good a cash return as good land under agriculture (Hickling, 1962). For fish culture the soil should be impermeable to water or be made so. Therefore, badly drained, water-logged soils are the best. Sandy soils will also be good provided they have a water holding impermeable layer just under them. Sandy soils produce the sweetest fish (Birtwistle, 1931), a. Pond Bottom The productivity of a pond is related to its bottom. The normal bottom of older ponds has two distinct layers: (1) the mineral ground floor or the original bottom, and (2) the overlying colloidal mass of organic mud which is the result of metabolic processes within the pond. 139 Metabolically, the task of the whole bottom is three- fold: (1) emission of nutritional matter from the bottom into the water; (2) fixation and chemical combination of allochthonous and autochthonous nutritional matter; and (3) offering shelter and food to bottom fauna, especially to mud dwellers. The pond muds can again be divided into two layers, namely, the more or less thin oxidizing layer over a thick reducing layer. As long as there is any oxygen in the water, the over—lying water is sealed off from the reduced mud by the oxidized layer, but, in the absence of oxygen in the water, the reduced layer may reach the surface and build up an oxygen debt. If the soil is rich in sulfur, dangerous conditions for fish could appear (Hickling, 1962). Ferric hydroxide in the pond mud is mainly responsible for the formation of oxidizing layer blocking the free ion- exchange between mud and water (Mortimer, 1941-1942). If oxygen Supply is cut off from the oxidizing layer, the re— duced iron cannot hold the absorbed ions such as phosphates and silicates. Consequently, they are diffused into the water and utilized by plants and thence by fish. The release of nutrients absorbed in the pond mud can also be brought about by liming. When the pH of the water rises from 5 to 7 and then to alkaline side, the ion absorp- tion capacity of mud falls (Ohle, 1938). Very little investigations on the physico-chemical 140 properties of soil and water of fish ponds have been carried out in Pakistan. The soil is generally alluvial but varies in structure and physical conditions in different parts of the country. It is generally alkaline in reaction and defi— cient in organic matter and nitrogen (phOSphorus and potash being adequate) in West Pakistan and in lime, phOSphorus and humus in East Pakistan where it is acidic in nature (Siddique and Mohammad, 1951). Accurate information on the optimum properties of soil and water for the culture of different species of fish is highly desirable. A classification of water, based on its capacity for the production of fish food and the level of natural or artificial replenishments in terms of nutrients needed to maintain them in a state of optimum productivity will be of immense help in putting the fish culture on a scientific basis. b. Drying the Pond Bottom The importance of drying the pond bottom was early recognized by the Chinese fish culturists. Fish ponds should be wholly drainable, and they must in fact be drained to col- lect the whole crop of fish. At this time, the pond may be left to dry for a while. Drying kills many harmful insects, fish parasites and disease bacteria. During the drying peri— od, the routine maintenance work of the pond like repairing the banks, drainage channels, etc. will be easy. The chief advantage, however, is the restoration of the pond. Wunder 141 (1949) states that (1) during the dry period, the accumulated organic matter in the pond bottom is completely oxidized and the contained nutrients released, and (2) on the dry bottom, plants will soon grow, and when the pond is refilled, these plants decompose and provide a good medium for the develop- ment of fish food. Schaperclaus (1933) and Huet (1960) also mentioned the mineralizing effect of the exposure of pond bottom to the Sun. Draining may cause the loss of fish food material, but it is off—set by the fact that the plankton organisms have resistant Spores, and many insect larvae can burrow in- to the pond mud. As these creatures grow very fast, they Soon repopulate a pond when it is refilled. During the dry period, which generally falls in late Spring and in Summer, quick growing leguminous plants may be grown in the pond bottom. This will (1) thoroughly dry out the soil and aerate it by the growing roots of the plants, (2) give the farmer additional income from the plants, and (3) increase the productivity of the pond if the crOp is ploughed into the bottom as a green manure. 4. Aquatic Organisms and Their Management The aquatic organisms of a pond include its phyto- and zoo—biota. 142 a. Phytobiota These include bacteria, planktonic and sessile microscopic and macroscopic algae and also submerged, float- ing and emergent macrovegetation. Bacteria.—-The important and useful functions of bacteria consist in dissolving (mineralising) dead remnants of organic substances upon which all vegetation depends. Lack of bacterial activity will lead to peat and morass con- ditions. They are abundant in tropical waters and may either be free-living, attached to higher organisms or are present in the pond bottom. Phytoplankton.--Phytop1ankton has two functions: (1) it is used as feed by the zooplankton and fish, and (2) it creates the productive, fine colloidal slime at the bottom of the pond. Phytoplankters may be either net-plank- ton or nonnoplankton. The latter can pass through a net of even the finest meshes (0.064 inch mesh), but the former cannot. Algal forms like Oedogonium, Spirogyra, Aphanothece, Aphanocapsa, Oscillatoria and Lyngbya may be seen in large or small quantities in a pond throughout most of the year. Phytoplankters have two blooms a year—~a lesser one in hot weather and a greater one during-the cold weather. The cold season is favorable for the growth and reproduction of a number of green filamentous algae like Zygnaema, Spirogyra, Bulbochaete and Oedogonium. Desmids, Chlorococcales, and p 143 some blue-green algae like Anabaena occur abundantly during this season. During the hot season, most of the desmids disappear and the blue-greens predominate along with Euglena of the family Eugleniaceae. During the period of heavy rains, algal growth is at a minimum (Hora and Pillay, 1962). PhytOplankters are detrimental to the metabolic cycle only during water bloom. Water bloom creates turbid- ity and cuts down light penetration. The decaying water- bloom through its oxygen consumption and release of toxins may also be injurious to fishes (Prescott, 1948; Ingram and Prescott, 1954). Macrovegetation.--Macrovegetation in a pond may be best divided into the three classes of: (l) emergent plants; (2) floating plants; and (3) submerged plants. The follow- ing emergent plants are of importance in a fish pond in East Pakistan (Anonymous, 1957; Chokdar, 1958): Water lily (Nymphaea Spp.) Prickly water lily (Euryale ferox) Water primrose (Limnanthemum Spp.) (Ipomaea reptans) (Jussiaea repens) Water chestnut (Trapa bispinosa) (Trapa natans) Water milfoil (Myriophyllum Sp.) (Limnophyla heterophylla) Arrowhead (Monochoria hastata) (Sagittaria sagitifolia) Pondweed (Potamogeton spp.) .1314813." 144 The emergent plants are rooted in the bottom of the pond and their leaves and floral shoots rise above the water level. They grow more abundantly in the shallow parts of the pond. They are noxious from the view of pond culture and for the following reasons (Schaperclaus, 1933; Sarig, 1957): l) 2) 3) 4) 5) 6) 7) 8) They cause bottom deposits by sinking down to it at death. They shade the water to such an extent that the development of the fish and productivity of other aquatic organisms are noticeably retarded. They often reduce the oxygen content of the water. They hinder fish in finding their food. They deprive the pond of valuable plankton. They penetrate the bottom extensively with their roots and reduce the productive layer of decom— posed matter. This further reduces productivity. They make cleaning and prOper supervision of pond more difficult. Predacious fish also find hiding places in them. They increase mosquito menace. However, a moderate growth of these plants will increase the chances for the development of 200plankton. The following floating plants are important: Water hyacinth (Eichhornia speciosa) Water lettuce (Pistia stratiotes) Duckweed (Lemna minor) (Wolffia arrhiza) 145 Water velvet (Salvinia natans) Pondweed (Azolla pinnata) Of these, water hyacinth and water lettuce are the most im- portant. These plants float on the pond surface and are rooted in the water. They are harmful since they Shade the pond almost completely without offering any compensating advantages. Under the submerged plant category comes all the weeds which chiefly grow beneath the water surface. The important submerged plants are: Bladderwort (Utricularia stellaris) Coontail (Ceratophyllum demersum) Tape grass (Vallisneria spiralis) Pondweed (Hydrilla verticillata) (Ottelia alismoides)7 (Naias Spp.) (Lagerosiphon Sp.) (Chara Spj) Submerged plants are rather helpful for the following reasons: 1) They are the natural food of many animals in the pond. 2) They largely Support the pond with necessary oxygen. 3) They are the ideal haunts for the herbivorous fauna. 4) The decayed plants are a good fertilizer for the following year. An excessive growth of submerged plants will however become 146 noxious. It will shade the deeper layers of the water thus creating difficulties for the fish to find food. It will reduce the oxygen content of a pond at night. b. Control of Phytobiota Algae Preventive measures.-—Fertilization of ponds should be avoided when growth is excessive. Curative measures.——(1) Mechanical—-Limited water areas can be cleared by means of nets and Screens. (2) Biologica1—-Introduction of algivorous fishes like Tilapia. (3) Chemical--Copper sulfate at the rate of 1—2 p.p.m. is quite effective. A higher concentration than this may be toxic to fish. A great defect of chemical control is that the dead algae cause oxygen depletion during decay (Prescott, 1948; Kessler, 1960). It is advisable to use copper sulfate at least a month before the bloom is expected. Macrovegetation Preventive measures.-—Shallow ponds encourage the growth of rank vegetation. Removal of excess mud, and deepening of pond will decrease the weed growth considerably. Curative measures.--(1) Manual labor--Control by this method has been found Suitable and economical in fish ponds in the case of floating plants like Pistia and Eichhornia (Ahmad, 1955). Nymphaea can be stOpped growing by repeated underwater cutting of stems. (2) Shading-—Submerged plants 147 like Ottelia can be controlled by shading it with Pistia. Prevention of photosynthesis by shading may also control Hydrilla, Naias, Vallisneria, Ceratophyllum and other vegetation. (3) Biological-—Weed control by herbivorous exotic fish Tilapia is not yet successful in small ponds of East Pakistan. However, it is too early to draw any definite conclusion regarding this. Schuster (1952a) indi- cates that Tilapia and the Chinese carp (Ctenopharyngodon idellus) are highly successful weed controllers in Indonesia. De Bont (1949) observed that Tilapia can clean up satisfac- torily the semi—emergent vegetation in ponds. Van der Lingen (1957) found that ducks are very effective in controlling pondweed. They clear the pond, manure the water and provide income from the meat. He also got better fish crop with ducks in the pond. (4) Chemical control--Fertilization: In the South-East United States, fertilization is a profit- able way to control water weeds. Besides darkening the water by increasing turbidity, it increases the fiSh food. This results in greater fishing success and higher yields. Highly fertile waters grow millions of microscopic algae. These shade the pond bottom and prevent the seeds of water weeds from germinating and growing. Usually, 800-1200 pounds of 8N-8P-2K fertilizer are applied per surface acre of pond in two to three applications per year (Davison E£_El-1 1962). In East Pakistan, lON—8P-4K fertilizer was found to 148 produce sufficient Microcystis to form a thick cover after four applications in two months, first at the rate of 5 p.p.m., then at 10 p.p.m. (Anonymous, 1958). Submerged weeds can be suppressed temporarily by ploughing in a high dose of a mixture of copper sulfate and ammonium sulfate during the drying period. SuperphOSphates at the rate of 500 p.p.m. are effective against Hydrilla, Hormone weedicides: Fernoxone (sodium 2,4-D) at a concentration of 2 p.p.m. is effective in killing submerged plants like Hydrilla, Naias and Potamogeton and floating plants like Pistia and Eichhornia without any adverse effect on fish or other pond biota. Planotox (ester of 2,4-D in liquid form) is effective on various submerged plants when Sprayed at the rate of 9—10 p.p.m. Sodium arsenite: It is very effective in concentra— tions of 5 p.p.m. in completely destroying several submerged weeds like Hydrilla, Ottelia, Ceratophyllum, and the alga, Spirogyra, in about two weeks without any adverse effects on carps, Tilapia, catfishes, and Snakeheads. It is a dangerous caustic poison and Should be used with caution. It may also reduce fish food production (Anonymous, 1958). Chemical control of aquatic weeds cannot be recom- mended for ponds whose water is used for domestic purposes as well as for watering the livestock. 149 c. Zoobiota Zoobiota consists of floating, attached and bottom dwelling organisms. Copepods, cladocerans, rotifers and flagellates constitutes the main microfauna. Zooplankters exhibit a seasonal periodicity in their abundance similar to that of phytoplankters. Zooplankters have a great role to play in the productivity of a pond in the sense that they form the major portion of food of the young fish. Among the macrofauna, worms, molluscs, crustaceans, and insects are of importance. Extraneous fishes are either weed feeders or predatory. Control of zoobiota in nursery ponds has been dis- cussed elsewhere. Some weed fishes are larvivorous and help check the breeding of malaria—bearing mosquitoes. Khan (1947) observed that Colisa fasciata, Ambassis baculis and Barbus sophore can each eat 148, 136, and 90 eggs of Anopheles per day in the Punjab, West Pakistan. Similar findings were also reported by Ahmad (1958) from East Pakistan. Hofstede and Botke (1950) observed that Tilapia mossambica could reduce the mosquito menace in some Javanese ponds by controlling the floating filamentous algae on which mosquitoes lay eggs. Fishes like the snakeheads (Ophicephalus spp.), cat- fishes (Wallago attu, and Clarias batrachus) and the climbing perch (Anabas testudineus) are probably the most destructive predacious pond fishes. There is no adequate way to estimate 150 the losses caused by these fishes but the damage is probably considerable and for the following reasons: 1) They exploit much of the natural food of the pond. 2) They prey on fry and fingerlings of the cultivated carps. 3) They help in transmitting diseases and parasites. d. Control of Predacious Fish Preventive measures.--(l) Periodic draining and cleaning the pond. (2) Screening the inlet of the pond before the onset of the monsoon. (3) Repeated fishing. Curative measureS.—-These are inadequate in those ponds which cannot be drained. Besides, predacious fishes are extremely hardy, and can even survive drought by burrow— ing deep into the wet mud. Use of toxins: Numerous types of toxic chemicals are now in use to clear fish—bearing waters of undesirable fishes (Applegate et al., 1957; Bridges, 1858). The best known fish toxin is rotenone, contained in Derris elliptica and D. uliginosa. It is generally agreed that a concentra— tion of 0.5 p.p.m. rotenone by weight is lethal to most kinds of fish. It does not penetrate the deeper depths of pond or lake when applied at the surface. Water temperature should be at least 750F at the surface for best results. Rotenone—treated fish reacts as follows: 151 l) Constant gaSping and gulping of air. Rotenone does not deplete oxygen but the fish cannot utilize it because the passage of the oxygen— bearing red blood cells (R.B.C.) has been effec— tively blocked by the constriction of the capil- laries in the gills. 2) Loss of equilibrium. The cessation of the passage of the R.B.C. cuts off the supply of oxygen to the brain with a consequent loss of function of the organs of equilibrium. 3) Fish can recover fully from the effects of rote- none narcosis within a few hours (Krumholz, 1948). Rotenone poisoned fish may be used for human consumption (Sarig, 1954). Alikunhi (1957) observed that at 20 p.p.m., the toxicity of derris powder persisted for 8—12 days at Indian temperatures, while lower doses up to 6 p.p.m. per acre did not make water toxic for more than four or five days. Mohanti and Mohanti (1950) observed that 5 p.p.m. hydroquinone could kill all the carps and catfishes in 2—6 hours, but most of the snakeheads remained alive at this con- centration. Hydroquinone depletes oxygen, but it is restored within 20 hours. It does not affect phytoplankton. Nowadays much more potent toxins are available. They are primarily insecticides and when they are used in rice fields, they kill or threaten fish culture there (Edmondson, 152 1959; Kuroda, g£_gl., 1956; Matida and Kimura, 1957). Soong and Merican (1958) observed that endrin at 0.008 p.p.m. used in the form of emulsifiable concentrate called endrex cleared the pond thoroughly. It is cheaper than derris root. It is particularly useful in dealing with large bodies of water 10 to 30 feet deep where the cost of piscicides used is an important consideration. The fish killed with endrin is not toxic to human beings. The toxic effect of endrin is dissipated in 2-5 weeks after which the pond may be restocked. Before using such powerful piscicides, all the fish that can be caught by other means will be re- moved for sale. All precautionary measures need to be taken before powerful piscicides are applied. The pond must not leak to allow enough toxins to escape into public waters killing fish there, as this may lead to prosecution. Birds like cormorants, eagles, herons and kingfishers, and snakes and others are not pond dwellers but they feed mainly on fishes. They may be either Shot or caught by set- ting traps. 5. Preparation of Pond for Stocking a. Preliminary Steps The preliminary steps in the preparation of a pond for stocking are: (l) checking inlet and outlet arrangement; (2) repairs or improvements; (3) control of undesirable 153 aquatic biota; (4) correction of physico-chemical properties of water and soil; and (5) draining and desilting. b. Liming Demoll (1925), Schfiperclaus (1933), Walter and Nolte (1930) and Wunder (1949) devoted many pages to liming ponds. In general, calcareous waters with alkalinities of more than 50 p.p.m. are most productive of fish. Waters with alkalinity of less than 10 p.p.m. rarely produce large crop (Mortimer and Hickling, 1954). The beneficial effects of liming has been attributed to various factors, including the direct utilization of cal- cium as plant and fish food (Adan, 1935). These are: l) The production of neutral or alkaline reaction in a formerly acid medium. 2) The Speeding up of the decomposition processes in the muds. 3) The establishment of a strong pH buffer system. 4) The production of bicarbonate-CO reserves, so 2 that CO lack cannot be a limiting factor. 2 5) Counteraction of possibly poisonous effects of excess magneSium, potassium or sodium ions. 6) Base-exchange phenomena and flocculence effects in muds which liberate other absorbed plant nutrient into the water. 7) Fixation of harmful organic and inorganic (humic) acids. 154 8) Poisoning competitors and enemies of the fish. 9) Disinfection of the pond against disease. Liming is an essential preliminary to successful pond manuring. Lime is generally applied in the form of ground limestone (CaCO3) slaked lime (Ca(OH)2) or quick lime (CaO). Calcium carbonate becomes calcium bicarbonate by slow dissolution. Quick lime is more advantageous as it produces the same results in a pond with half the quantity in terms of weight. Lime can be applied on the pond bottom, added to water at the inlet or just be spread on the water surface. For best results, quick lime should be applied after drain- ing, and the pond should be allowed to dry for about two weeks. A dosage of 200 kg. CaO per hectare has been recom— mended; a quantity of 1000-1500 kg. CaO will be required for ponds with acidic soil and water (Hora and Pillay, 1962). Schaperclaus (1933) suggests the following dosage (Table 20). Macan §£_31, (1942), however, suggested the following doses (Table 21). Swingle (1947) reports that the addition of lime— stone to ponds receiving inorganic fertilizers always g3- creased fish production in experimental 1/4 acre ponds. He considers that the quantity of CO2 may be a limiting factor in fish production in ponds with inorganic materials, acting through the food chain which begins in most cases with phyto- plankton production. He may have had PO 4 complexing with 155 TABLE 20. pH of soil and approximate quantity of CaO required to neutralize it pH of soil Lime requirements in doppelzenter (dz.) or 200 kg. CaO per hectare Heavy loams Sandy Sand or clays loams Less than 4.0 40.0 20.0 12.5 4.0—4.5 30.0 15.0 12.0 4.5-5.0 25.0 12.5 10.0 5.0—5.5 15.0 10.0 5.0 5.5-6.0 10.0 5.0 2.5 6.0—6.5 5.0 5.0 0.0 1 dz. = approximately 2 cwt; 1 dz/ha = 89.2 lb/acre. If limestone is to be used, the doses should be double. a Source: Schaperclaus (1933). 156 TABLE 21. pH of mud and limestone requirementsa pH of mud Calcium carbonate required (100 kg. per hectare) Less than 4.0 60-120 4.0-4.5 48—96 4.5-5.0 36—72 5.0-5.5 30-48 5.5-6.0 16-30 6.0-6.5 14-16 If slaked or quick lime is to be used, the above amounts should be multiplied by 3/4 or 1/2 reSpectively. aSource: Macan et a1. (1942). 157 CaCO3 to tie up PO as insoluble salts. 4 c. Fertilization The fertilization of fish pond is necessitated by the fact that there is a constant consumption of nutrient in it. .Periodic draining helps the fish culturist in mobiliz- ing the nutrients in the pond soil by drying and mineraliza— tion. But in intensive fish culture, it is often necessary to apply fertilizing agents to the pond to enhance its pro- ductivity. Just as in agriculture, organic and inorganic fer— tilizers make additional production of fish possible that cannot be obtained without fertilization. In Pakistan, cow dung, poultry manure, Spoiled oil-cakes, green grass and pondweeds are commonly used as organic manures. Inorganic fertilizers like sodium nitrate, ammonium sulfate, ammonium superphOSphate and their standard mixtures, commonly known as N-P—K fertilizers, are rarely used as manures in fish ponds. Researches on the use of manures in ponds are yet to begin in Pakistan. Pioneer investigations in Central Europe and North America regarding pond fertilization have been summarized by Neess (1949) and Swingle (1947) reSpec- tively. These investigations have yielded valuable informa— tion on the effect of fertilizers, eSpecially N-P-K fertiliz— ers, under conditions existing in temperate climates. It has 158 been found that the fish carrying capacity of pond in Alabama has been increased 300-400% as a result of fertili- zation. Organic manures.--Traditional practices of fertiliz- ing fish ponds with cow-dung, stable manure, poultry manure, oil-cake, green grass, dry leaves, etc. are in vogue in East Pakistan. Such combination of different materials of animal and plant origin ensure C-N-P—K balance through putrefaction, whereas organic fertilizers supply only N—P—K and their nu— tritive value is soon dissipated (Hora, 1951). The practices of using banana juice and soap waste in ponds are helpful in building up a reserve of readily available bicarbonate alkali. Banana stem has been found to contain a large amount of bicarbonate ion (Hora, 1951). Organic manures use up a considerable amount of dis— solved 02 during decomposition. .Major carps can live for 24 hours in water devoid of CO and containing 1 p.p.m. O 2 Another benefit of using organic manures is that organic 2. carbon retains nitrogen in the medium for a longer period. Green grass, dry leaves and rice straw are helpful in supply- ing silica and iron for the production of diatoms and other algae which are the food of many cultivated fishes. Saha §£_31. (1951) estimated moisture, N, protein, Ca, P, and K in 10 organic substances used as pond fertiliz- ers in West Bengal, India. Of the materials analyzed, fish meal containing 7% N appears as the richest source of N, 159 followed by mustard seed-cake and water hyacinth (Eichhornia crassipes), with 4.76% and 4.0% reSpectively. With regard to Ca, crab meal is the best source containing 12.3%, fol- lowed by Hydrilla, fish meal and Ceratophyllum with 4.8% 3.0% and 2.6% reSpectively. Ceratophyllum is very rich in P, 3%. With regard to K, banana leaf and Arum stem are the best sources containing 5.1% and 4.9% respectively calculated as K20, and then comes the water hyacinth with 4.2%. Fish meal, crab meal and mustard seed-cake will be quite costly for an average pond owner. Water hyacinth, Hydrilla , and Ceratophyllum are found abundantly in fish ponds, lakes, swamps and canals. These may be collected, dried or composted. To these may be added sufficient quan- tities of similarly dried or composted banana leaves and Arum stems. This will be a good fertilizer for ponds in rural areas. The disadvantages of using organic manures are two: (1) they stimulate heavy growth of aquatic vegetation retard- ing fishing efficiency, and (2) during hot weather, the rate of decomposition may be so rapid as to deplete oxygen and saturate the water with C02, resulting in the asphyxiation of fish. In the application of organic manures, it is neces— sary to balance the oxygen budget and the oxygen concentration should not be below 3 p.p.m. Ordinarily, a dose of 1000 kg. of cow-dung or horse manure per hectare is recommended. Where cow—dung, sheep or 160 poultry manure are not available, compost can be used as a substitute. Any available plant matter like leaves, grass cuttings, aquatic weeds, etc. can be composted which will be ready for use in about three months. About 5,000 kg. per hectare may be needed to give rise to a sufficiently abundant growth of fish food in ponds. Inorggnic fertilizers.--The important fertilizing elements can be supplied to a pond by the application of N—P-K (6—8-4) fertilizers. A number of formulae for inorgan— ic fertilizers for fish pond manuring have been evolved and the following two have yielded good results in the United States (Swingle, 1947): l) 100 kg. of 6N-8P-4K and 10 kg. of sodium nitrate. 2) 100 kg. of ammonium sulfate 150 kg. of superphOSphate (16%) 12.5 kg. of muriate of potash and 37.5 kg. of finely ground limestone. A mixture of organic and inorganic manures consisting of three parts of animal manure and one part of superphOSphate per hectare per annum have also been found quite effective (Hora and Pillay, 1962). Fertilizers, organic or inorganic, are most effective if they are applied after draining the pond. If it is not possible, they can be applied from a boat. The first applica- tion can be made after the monsoon. Several applications will cause a plankton bloom and if the turbidity is such that it 161 makes a Secchi Disk disappear at a depth of about 45 cm., the pond is considered properly fertilized. Ball (1949) reported that inorganic fertilizers increased planktonic fish food in some Michigan lakes by as much as 3.3 times. 6. Stocking In pond culture, the production of fish is the main objective and the selection of Species will depend on the conditions under which the fish will have to live and grow. For instance, the type of food available in the pond and its general biota would determine the association of fish to be introduced into it. For practical purposes, a pond can be divided into surface, midwater and bottom zones. The surface feeding Species can be plankton feeders or they can take floating vegetation. Similarly, a bottom feeder may live on snails, worms and insects or organic debris. In selecting Species, one must bear in mind the following points: 1) The Species should be tolerant of one another. 2) They should not compete for food with one another. 3) Between themselves, they should use up all kinds of available food materials in the pond and there— by contribute to the general sanitation of their environment. It will thus appear that proper stocking not only means selection of Species but also the number of each kind depending upon the extent and nature of fodder resources of 162 the pond. Artificial feeding of pond fish is almost nil in Pakistan, therefore stocking methods should be devised in such a way that the fish can grow healthy with the food pro— duced in the pond naturally or through fertilization. To evolve sound stocking techniques, the basic information neces- sary is the food requirement (quantity of food consumed per unit time) of different age or Size groups of the fish and the quantity of fish food that is or could be produced in the pond. Stocking Systems in East Pakistan are now based on trial and error as the above type of information is lacking. Based on the expected growth increment, the total production and the expected mortality figures, the number of fish to be stocked can be computed as follows: Number of fish : Total expected increase in weight to be stocked Expected increase in weight of individual fish For example, if in a pond of one hectare area, a total pro- duction of 1,000 kg. of carp can be obtained and it is to be stocked with fingerlings of 30 g. weight with a view to har- vest the fish when they have attained a weight of 330 g., the expected mortality being 10%, the number of fingerlings to be stocked will be: 1,000/0 3 + 100 = 3,433. The four major carps (Catla catla, Labeo rohita, 163 Cirrhina mrigala and Labeo calbasu) are profitably cultured together, since 93313 is a plankton feeder, rohu column feeder, mrigal debris feeder, and kalbaus mollusc feeder. Alikunhi (1957) suggests that in Bengal (East Pakistan and West Bengal, India) 30% 93313, 30% rohu and 40% mrigal may be stocked in ponds. Satisfactory results are obtained when these three Species are stocked in equal numbers at the rate of 3,000 per acre. At that density of stocking, rohu and mrigal grow quickly but 93313 grows slowly when the density of stocking exceeds 1,000 per acre. The general yield varies from 1,500 to 2,500 pounds per acre per annum depending on climatic conditions. Hora and Pillay (1962) write that allowance should be made in the stocking system for an annual mortality which may be more than 30%, also losses by reduction in the volume of water in the pond as a result of evaporation during summer which may be computed as about 10%. A proportion of 30% 93313, 60% rohu, and 10% mrigal is considered very profitable. In a pond of one hectare in area, about 1,875 Catla, 3,750 rohu and 625 mrigal, all 8 to 10 cm. in length may thus be stocked. If kalbaus is included, rohu may be decreased to 50%. AS regards other cultured fishes, a stock density similar to that adopted for 'Qgtla, rohu and mrigal is recommended though the optimum is not yet determined. Considering the natural food supply, the following stocking rates are suggested by Ahmad (1957a) for East Pakistan's fish ponds (Table 22). 164 dumm> non whom non 6H0fi> pmpudeo one meson mo mnaxUOHm mo ovum .NN mqm¢H 165 .ewawanoe .Amkmoav emea< ”mousomm OH . . . . . . anus mo “mom ma . . . . . . . . new» mo ummm ma . . . cowposooupcfi Hmumm OH nowpusooupcfl Hopma space pcm demos “ma ”pm Umpmsfipmm mmoq $¥t mm coapusooupna umpmm nucos ywa ”um Umgmsfiumm mmoq $4 RLNFI. mhhll. ppm amaoe me moa mm mnmnamx coaumpmmm> w Hmmfiuz uwpmnvm mu OHH cm snom >um #50 oem ms woa mm mapmu unumz uwosa< >663: mmwll .meII ppm Hayes mma Hmm mm mswnamm pcmoasnm a Hume“: mpcwfla momma: mma Hmm mm seem no: coaxemad owv NMH woa om «demo Honuwmz unmao omo coo be. Hmon mmma >Hm>flp owa wwm om mannamm nmumqsoo no» a Human: IEGMH909>£Q owa wmm om seem .pcmauamm2m omk mum «mm ow «Humo :Ouxcaadoom Emaczoam mww bMMhH ppm fiance oom Nov om mammamz Houpqoo moon: . s Mammy: Hahpcmauamwsm oom mow mm seem mpemad 0a coo vow com om «sumo -pmsvw “mamam meao E E blow :38. ovm oom om mamnHmM a Hmmfluz couxcwad mo com ovm om anon oucmpcsnm ov¢.H 000 000 on «demo “commeHmm nmflaoouw A.mnav Aumnsscv Aumnsscv g caow> um>o paw mcoa mcoa Hmzccm .ma 0 mammott .zfi mnv manque UmeOpm on o» cowpmpmmm> amps: popomdxm swam mo mmfiumdm mo unaumz _p:oa mo Hoaoo 166 7. Metabolism and Growth a. Food and Feeding Pond-fish culture differs from fisheries in natural waters in that basic production capacity of the pond may be augmented through fertilization and pond care, or the natural food may be supplemented with artificial food. In both cases, a knowledge of the basic nutritive requirements of the pond fish is required. Metabolism of pond-fish consists of two components: part of metabolism serves to sustain the body of the fish and its functions and the rest takes care of growth and further development. The second function is the primary concern of the pond owner (Schaperclaus, 1933). The ratio of food consumed by the fish to the fish flesh produced is called forage ratio. The term ”food quo— tient" expressing the unit weight of the fish food required to produce a unit weight of fish flesh denotes the same idea and indicates the commercial value of the fish foods. §g§ also Lagler (1956). The food requirement of a fish (by weight) is often judged by what is known as the sustenance ratio which can be obtained by the following formula: 2 Crude fat x 2.25 + carbohydrate Crude protein Sustenance ratio 167 Sustenance ratio varies with age. Cultivated fish can be broadly divided into three categories: (1) those with low sustenance ratio of the order of 1:2 to 1:4; (2) those with medium ratio of about 1:5 to 1:6; and (3) those with high ratio of 1:8 to 1:12 (Schaperclaus, 1933). Such a classifi- cation of fish is not yet available in Pakistan, but it is Supposed that the major carps belong to the second and third categories. There is an important difference between natural food on which major carps largely depend, and the artificial food which is relatively low in protein content. The rela- tion between the nutrients plays an important part in their utilization by and growth of the fish. In the natural feed— ing, the ratio of food to fish (by weight) varies mostly from 1:1 to 1:1.8, while in the artificial feeding considerably lower ratios are met with (Mann, 1961). Carps cannot utilize animal protein since they have anatomically or physiologically no stomach. The extent of fat solubility and utilization is unknown. Fat content in the food, natural or artificial, is rarely above 2%. Carp can utilize 60-70% fat—free extractives. In plant foods, the content of crude fibers plays an important role. It is digested by carp up to 60%, presumably not through enzymes of their own but with the help of sym- biotic microorganisms. Chitin is not digested. As to the role of minerals, very little is known, although it is 168 obvious that calcium is important for bone formation. Mann (1961) writes that the type of food also plays a part. In artificial feeding of common carp, mincing is important. If, for example, lupine seeds were finely cut, the utilization of protein was 84%; when more finely chopped, it rose to 93%. The digestibility of protein is reduced when the food is overcooked, or submitted to excess heat in drying. The individual characteristics of the fish as race, age, etc. have a certain effect on the fat deposition in the body. The larger the fat accumulation, the better the nutri- tive requirements are met. The degree of food conversion into fish flesh depends on a number of factors, the most important being temperature. Fish, being cold-blooded, follow, within certain limits, Van't Hoff's Rule of Q10 in consumption of energy. An increase in temperature by 100C almost doubles the energy metabolism. In the same way, growth is related to temperature, an increase in rate taking place only as long as the optimum is not reached. In pond cultural practices, three types of fish are recognized: (1) those that relish and grow well on artifi- cial foods, (2) those that grow best on a diet composed of both artificial and natural foods, and (3) those that take only natural foods. ‘Qgtlg, rohu and mrigal belong to the second category. In selecting food for feeding, its dietetic 169 value and the economic practicability of its use in commercial fish culture must be considered. Schaperclaus (1933); Bondi .S£_Ei- (1957); Tamura (1961) and Hickling (1962) have dis- cussed in detail the artificial fish foods and their nutri— tive values. b. Growth In pond culture, growth is measured in terms of con- version efficiency (ratio) which indicates how many food units are required to obtain one unit of fish flesh. Growth can slow down or stop completely under unfavorable natural con- ditions when food supply meets merely the sustenance needs, evidently without any harmful effects on the fish. Overfeed- ing does not enhance growth above certain limits, only some reserve substance such as fat or glycogen is deposited. Con- sequently, fattening, as used in the rearing of land animals cannot be applied to fish. Besides, an increased fat accumu- lation, in general, is not desirable in fish flesh. On the other hand, in starving carp, the weight reduction takes place primarily at the expense of fat, later protein in mus- cles and viscera may also disappear (Schaperclaus, 1933). The lowering of feeding intensity or the non—availability of certain types of food often affect growth considerably. The density of fish population in a pond is a very important factor which influences the growth rate. Overcrowding causes competition for food and Space. Yashouv (1958) and Rose 170 (1959) have shown that greater concentration of excreta resulting from overcrowding is a growth retarding factor. Kawamoto £1_gl. (1957) have shown that growth of fish is much quicker in understocked ponds than in overstocked ones. From the practical point of view, there is a limit to the density with which fish can be stocked in ponds; for, beyond a certain limit, the gain due to a larger growing pop- ulation is off-set by the slower individual growth in Spite of an excess of food. This limit has been called "carrying capacity" by Yashouv (1959, 1963) who defines it as the bio- mass of fish that can be supported in a pond. Van der Lingen (1957) has called it "maximum standing crOp" which, according to him, is the maximum weight of fish that can be sustained by a pond, this weight of fish being at balance, without gain or loss in weight, with the food produced by the pond or made available to the fish. The maximum standing crop varies with many factors: 1) It will vary with the management of the pond. Yashouv (1959) writes that the productivity of a pond is deter- mined by its carrying capacity and by the time of growth of the fish biomass up to the level of the carrying ca- pacity. It does not describe the features of the pond itself, but rather the character of their management. Fertilizers with or without artificial feeding increase the carrying capacity of the pond. 2) It varies with the species of fish. It will be lower 171 where a fish is stocked which has a natural check in its rate of growth. It will be higher with herbivorous fish than with the carnivorous ones, because the latter get their primary vegetable food after 90% loss of the orig— inal calories in the body of the herbivorous. It will increase where two or more species of complementary feed- ing habits (cf. 93313, rohu and mrigal) are stocked be— cause the food available will be more completely utilized. 3) It will vary with water supply. Very shallow ponds do not support larger standing crOp of fish. 4) It will vary with climatic conditions. Growth of fish in temperate climates is generally less than that in the tropics. 5) It will also be affected by the size of the fish. A pond will support a greater weight of small fish than of larger fish, because the greater weight of small fish will have many more mouths to seek for the available food, and so make better use of the resources of the pond. To ensure a greater yield, fishing ("skimming”) from time to time is essential. Yashouv (1959) writes that the daily fish production decreases when the fish biomass ap- proaches the limit of the carrying capacity; it is advisable to remove some fast grown fish from the pond and start again with the small ones. In view of the fact that several environmental and other factors affect the growth rate of fish, it is rather 172 difficult to judge accurately the normal growth or even the maximum growth that can be expected for a particular Species. Data regarding the weights attained by some of the cultivated Species are given in Table 23. 8. Parasites and Diseases Many practical problems in the field of fisheries such as attempts to increase the productivity of ponds, to improve the stocks of valuable commercial fisheries in natural waters and most of all, to acclimatize fish in new localities require detailed knowledge of the parasites in— habiting the localities involved. It is equally necessary to know in what Species of fish and under what circumstances these parasites are able to live and thrive. Few investiga- tions in this important aSpect of fish culture have been undertaken in Pakistan. Diseased or abnormal fish occurs in nature but the diseases of fish bred or fattened in ponds are far more fre— quent and differ greatly from those inhabiting natural envi— ronments where their occurrence is not in an epidemic form. Among the most important factors facilitating the outbreak of diseases in ponds is the density of populations which is rather encouraged for economic reasons. Crowded ponds provide good conditions for the rapid Spread of diseases among the fish many of whom are usually of the same age. Con- sequently, when environmental conditions (water temperature, 173 TABLE 23. Annual rate of growth in weight of some cultivated fishesa Weight increase (g) during the year Species I II III IV Catla catla . 1,125—4,100 4,000-5,000 6,750 -—- Labeo rohita 900 3,600 5,400 -—- Cirrhina mriggla 650—1,800 2,600 4,000 ——— Labeo calbasu 450-800 ——- ——— _-_ Tilapia mossambica 140 ——- ___ ___ Lates calcarifer 1,500-3,000 5,000 ——— ——— aSource: Hora and Pillay (1962). 174 etc.) become favorable for mass reproduction of the parasite, the disease may Spread very quickly and, in a matter of days, the entire population of fish in a pond can be wiped out (Bauer, 1961). Again, there is always a risk of infection from wild fish which may gain entrance into the pond with the water during the rainy season. Such fish may carry infec- tious diseases. Birds flying from one pond to another may also carry infection. Good pond management can prevent or minimize the occurrence of disease and remedies are known for most of the common ones. Plehn (1924), Schaperclaus (1954), Davis (1961), and Dogiel 21.31: (1961) have written excellent books on the diseases of fish and their control. a. Ecology of Fish Parasites The animal parasites of pond fish are either external or internal. The plant parasites are generally fungal in character. The entire environment of an animal parasite is furnished by other living animals. It is not merely the host but also the host's environment that forms the environment of the parasite. This is eSpecially true for the ectoparasites. The composition of the parasite fauna depend on the geographical location of the habitat, the season of the year, the physico-chemical features of the water, the type of the bottom, and the fauna present in and around the habitat. 175 Besides, the direct area of activity and the environment of the parasite are also important. The character of the outer tissues of the host, the presence and the strength of the scales, the degree of development of mucus glands, the thick- ness of the subcutaneous connective tissue layer, all exert a continuous influence on the ectoparasitic fauna and a temporary one on those endoparasites which penetrate the host through the Skin (Dogiel, 1961). b. Deficiency Diseases These diseases may be caused by some vitamin defi- ciency in the food, or to some other upsetting factor. One such disease is anemia with very pale color of the gills, kidney and liver. The fish swim erratically and exhibit a high mortality rate. The remedial measures are good management of ponds, drying, liming, and removal of shading vegetation. The cure is to transfer the suffering fish to running water or to a new, well-prepared pond. c. Environmental Diseases Sluggish swimming, skin lesions, and discoloration of the gills may be caused in water with a pH of less than 5. The weakened fish may be attacked by fungi or skin parasites. The corrective measure is to lime the pond so as to increase the pH of the water to about 8. 176 d. Fungal Diseases Gill—rot is caused by Branchiomyces Sp. which is a filamentous aquatic fungus. The disease, which may readily kill the fish, appears as a red spot in the gills, turning their filaments later into graying white. This causes the fish to suffocate. The disease occurs during summer when heat and decaying organic matter coincide with a shortage of water (van Duijn, 1962). Molds of the family Saprolegniaceae may attack the skin, and sometimes the gills and eyes, of fish in which the resistance of these organs has been weakened by injury, by other parasites or such adverse conditions as an abnormal pH of the water. The infection is characterized by the growth of thin threads of dirty—white or grayish color from the infected parts, resembling tufts of cotton wool if growth of hyphae is abundant (van Duijn, 1962). .Sgg also Khan (1947). Valuable fish can be cured by suitable treatments with chemicals; phenoxethol and malachite green are at present regarded as the most suitable remedies (van Duijn, 1956). Schaperclaus (1954) writes that 12 kg. of c0pper sul- fate per hectare of pond surface with a depth of one meter will prevent the outbreak of the disease. The treatment should be 3-4 times a year during summer. 177 e. Bacterial Diseases Infectious dropsy is the worst bacterial disease of common carp, and is suSpected to be associated with Pseudomonas punctata. The symptoms of dropsy are swelling of the belly due to water, ulcer, deformation of the vertebral column and lengthening of the fins. .Bacteria also parasitize the peritoneal and Opercular cavities of the fish. Bacterial attack increases with the fall in temperature of pond water in winter (Bisset, 1948a). The preventive measures include screening of inlet of the pond against the entry of wild fish which may carry infection. The control measures are: collection and removal of diseased fish, breeding strains of carp resistant to the disease and injecting the fish with antibiotics (Snieszko, 1953). In studies of bacterial fish diseases the functional role of antibodies in fresh-water fish was revealed. The importance of this defense mechanism is staving off pathogenic organisms is evident and reasonably well established. Evi- dently this build-up of immunity may also check the growth of the normal flora (Bisset, 1948b). He also Showed that high temperatures encourage the development of immunity. Cushing (1942) established that carp (Cyprinus carpio) produced ag- glutinins more proficiently at 82°F (28°C) than at 59°F (15°C). 178 f. External Parasites Protozoa Pseudomonas rebae.-—This parasite is found on the gills of the fry of major carps. Tripathi (1954) reported that out of 50 Cirrhina reba he examined, 45 carried this parasite. Rohu, mrigal and Catla showed fewer infections. Trichodina indica.--This is the commonest ciliate parasite infecting the gills of pond fishes and their fry and fingerlings. Tripathi (1954) observed that among the major carps, its incidence varies from 50—90%, the highest being in rohu (Labeo rohita), and the lowest (13%) in kalbaus (Labeo calbasu). Among the snakeheads, the per- centage of infection ranges from 10-40%. Scyphidia pyriformis.-—It is found on the skin and fins of the fry of Labeo rohita. The fry of other carps are not infected seriously. Treatment: (a) Bathe in 2—3% salt solution for 10 min. (Tripathi, 1954). (b) Bathe in 0.01% potassium permanganate (Bauer, 1961); Allison (1957a) used 3 p.p.m. (c) Bathe in 1:4,000 formalin for one hour (Davis, 1961). Prevention: (a) Good flow of water in the pond. (b) Avoidance of very shallow ponds. (c) Liming the pond. Costia Sp.--It affects the epithelial cells and mucus ’glands of the fish, also attaches itself to gills, skin and fins of the host of all ages. It may kill only the young. Treatment: (a) Bathe in 5% salt solution for 5 min. (Bauer, 1961). (b) Bathe in 1:4,000 formalin for one hour (Davis, 1961; Fish, 1940). (c) Bathe in 2 p.p.m. pyridylmercuric 179 acetate (PMA) for one hour (Clemens and Sneed, 1958). .Prevention: (a) Disinfection of ponds and fishing gear with lime. (b) Quarantine of newly introduced fish. Chilodonella sp.-—This parasite attacks the gills, fins and body surface of the fish (van Duijn, 1962). Treatment: (a) Bathe in 5% salt solution for 5 min. (Bauer, 1961). (b) Bathe in 1:4,000 formalin for one hour (Davis, 1961). Prevention: (a) Deepening the pond. Ichthyophthirius Sp.—-This protozoa attacks the gills, fins, skin, and sometimes the eye of the fish of all ages. Treatment: (a) Bathe in 1:4,000 formalin for one hour (Davis, 1961). (b) Bathe in 2 p.p.m. PMA for one hour (Clemens and Sneed, 1958). (c) Holding the fish in swift—flowing water. Prevention: (a) Preventing the parasite-carrying wild fish from entering the pond. (b) Liming the pond. Monogenic Trematodes Dactylogyrus Spp. These trematodes attack the gills of the fish of all ages throughout most of the year (Jain, 1958). Gyrodactylus Spp. These attack the skin and fins of the host. Treatment: (a) Bathe in 3-5% salt solution for 5 min. (b) Bathe in a mixture of 7% NaCl and 30%MgSO4 solu- tion for 10 min. (Bauer, 1961). (c) Bathe in 1:4,000 formalin for one hour (Davis, 1961). Prevention: (a) Fingerlings should be checked before stocking. (b) Liming of the pond. Leeches Khan (1944) observed that the leech (Hemiclepsis Sp.) 180 attacks the lips, nostrils, gills, fins and anus of young and adult mrigal (Cirrhina mrigala), and rohu (Labeo rohita), in some ponds in Lyallpur, West Pakistan. Mortality is re— ported to be caused by it among the young carps (Saha and Sen, 1955). Treatment: (a) Bathe in 1:1,000 glacial acetic acid for one min. (Khan, 1944). (b) Bathe in 0.5% gammexane (Saha and Sen, 1955). (c) Bathe in 2.5% salt solution for one hour (Bauer, 1961). Prevention: (a) Draining and dry- ing the pond. (b) Liming the pond. COpepods Argulus sp.——This copepod is found mainly on £3222 rohita, though other major carps are also attacked. .Hora (1943) reported heavy mortality among carps in Bengal caused by it. Southwell (1915) also reported mortality among carps from the Punjab. Treatment: (a) Bathe in 1:1,000 glacial acetic acid for 5 min. followed by a bath in 1% salt solu- tion for one hour (Khan, 1944). (b) Bathe in 0.1 p.p.m. gammexane (Saha and Sen, 1955; Sarig, 1958). (c) Bathe in 0.2% lysol or 0.001% potassium permanganate solution for 5—15 seconds (Bauer, 1961). (d) Bathe in 0.01—0.02 p.p.m. DDT mixed with pond water (Schaperclaus, 1954). (e) Bathe in 1:4,000 formalin for one hour (Davis, 1961). Prevention: (a) Draining and drying the pond. (b) Liming the pond. (c) Keeping the embankments clear of roots of plants thus reducing the area of egg deposition by the copepod (Bauer, 181 1961). (d) Culturing larvivorous fishes like Colisa fasciata, Ambassis baculis and Barbus sophore in the pond. g. Internal Parasites Protozoa Nyctotherus pangasia.—-This ciliate parasite was reported by Tripathi (1954) from the intestine of catfish, (Pangasius pangasius). Though the infection was heavy, he did not observe any pathological effects on the intestinal wall of the fish. The curative and preventive measures for this parasite are not known. Platyhelminthes Trematodes that are parasitic in the internal organs of fish belong mostly to the genus Distomum with a life cycle including stages in mussels and snails. Cestodes (tapeworms) that are very risky from a hygienic point of view belong to the genus Diphyllobothrium. They generally remain dormant in fish until it is eaten by a human being. The latter is infected in case he fails to apply adequate heat treatment to the fish prior to consump- tion (van Duijn, 1962). Attempts (Allison, 1957b) to cure the fish suffering from these parasites have not been suc— cessful. General prevention of all fish diseases lies in the public Sphere; good sanitation will prevent the Spread of human excreta without disinfection or other cleaning measures 182 into free waters, and dogs and cats must be kept away from fish ponds. A healthy fish in a well-managed pond can be strongly resistant to all fish diseases (van Duijn, 1962; Hickling, 1902). 9. Capture and Marketing a. Capture Seines, cast nets and drag nets are used for this purpose in Pakistan (ESE also fishing craft and gear, page 25.) Intermediate fishing is conducted to catch fish for sale, it also serves the purpose of thinning out the stock of fast growing Species like 93313, thus quickening the growth of other fishes in the pond. Kawamoto ££_gl. (1957), how— ever, reports that intermediate fishing may reduce the growth of the fish remaining in the pond by as much as 5%, due to irritation, upset and alarm caused to them. At the onset of the rainy season, fish farmers flow in a good supply of rain water from a nearby source. There is a tendency for the fish to swim toward the inlet and col— lect at the mouth of it where they are caught by various bamboo traps as well as by cast nets. In this way minnows and other pond fishes are taken. Harvesting a pond by draining it is also practiced during summer. The fish tend to collect in the water remain— ing when the rest of the pond lies bare. They may also 183 collect in depression in the pond bottom. They are then picked up by hand or in dipnets. b. Marketing Pond fish can often be marketed in living condition. Live fish fetch a better price than the dead ones. Cat- fishes, the climbing perch and the snakeheads have labyrin- thiform accessory breathing organs enabling them to live out of water or in only enough water to keep their body and gills moist for about a week after the catch. .Sgg further fish marketing, page 50. I. Fish Culture in Lakesj Reservoirs, Swamps and Irrigation Canals Besides ponds, lakes, etc. are also used for fish culture, but their operations are quite different from those of pond culture. In expansive waters, introduction of cul- tivable fish is undertaken as a part of a general fishery improvement program rather than for fish culture in its truest sense. See also Zobairi (1953). l. Lakes and Reservoirs Lakes and reservoirs can play a significant role in food production provided they are improved and well-managed. Limnological studies of these waters have so far not been undertaken in Pakistan. Forel (1892), Welch (1948, 1952), Ruttner (1953) and Hutchinson (1957) have written valuable books on the limnology of lakes of temperate zone 184 from which useful information can be derived for limnolog- ical work in Pakistan and other tropical areas. Lakes and reservoirs differ greatly in size and depth. Their productivity is greatest in the shallow lit- toral zone. Thermal stratification occurs in deep lakes in summer and winter, but as most of Pakistani lakes are shallow, a true thermocline seldom develops in them. This enables continuous mixing of waters and circulation of nutrients. These account for higher productivity of these waters. .Bigtg.——Biota of lakes and reservoirs are more or less similar to those found in ponds. Reservoirs formed by the construction of dams across rivers will have riverine biota but will soon be succeeded by those adapted to still water Situations. According to Hubbs and Eschmeyer (1938), the major factors affecting the weed growth in lakes are: (1) lat— itude; (2) altitude; (3) topography of the bottom; (4) fluctuation in water level; (5) presence of harmful chemicals in the water; (6) turbidity; (7) productivity of water; (8) exposure to waves; (9) suitability of bottom materials; and (10) abundance of algae. .Excessive growth of weeds will be inimical to the normal life of the fish. Methods of weed control are sim— ilar to those applicable to ponds. 185 Lakes and reservoirs abound in extraneous and pre- daceous fish which form the major part of the fishery. The fish stocked in these waters must compete with the extra- neous fish. Selective poisoning by rotenone etc. may be conducted in these waters to remove the undesirable fish before stock- ing is initiated. Studies on the feeding and breeding grounds of these fish are necessary before any improvement work can be initiated. 2. Swamps Swamps are extensive shallow water areas with exces- sive weed growth. They are formed in the bed of dead lakes. Some have the same characteristics as rice fields. Very shallow swamps can be converted into ponds and be managed as such, while deep water swamps can be reclaimed for man— agement as lakes. Swamp fishes are very hardy and usually belong to air—breathing species. Predaceous fish are also found in large numbers. Fishing is relatively easy in swamps because of their shallowness. Reclamation of swamps in East Pakistan.7-The Direc- torate of_Fisheries, East Pakistan, has initiated a five— year project in 1957-1958 for the rehabilitation and develop— ment of 15,000 acres of fallow water areas in this province. For the sake of efficiency in operation, the entire area has 186 been divided into 90 units, each unit comprizing about 160 acres. Each unit is commercially self—sufficient and econom— ically independent, therefore, success or failure of one will not vitally affect the other. The expenditure incurred in the development work is expected to be recovered with profit from the proceeds of the sale of fish produced in these waters. Table 24 shows the swamps which were under development during 1957-58 (Ahmad, 1958). 3. Irrigation Canals Irrigation canals carry water from rivers or reser— voirs to agricultural lands. There is always a likelihood of marked variation in the water level in these canals. However, it may be found possible in suitable localities to partition off sections of a canal by means of bamboo through which water can flow freely but the fish cannot escape. Where this is not possible, an entire canal system can be managed as a single unit in which migratory fish can be cul- tured. 4. Stocking Any cultivated fresh-water fish can be stocked depend- ing on their availability, local demand, and profitability. Introduction of exotic fish like Tilapia Spp., Puntius javanicus, Cyprinus carpio, and OSphronemusggourami may be considered here. 187 TABLE 24. Development of swamps for fish culture in East Pakistan, 1957-1958 Name of Area Cost Estimated Estimated District fish pro- income duction in 1962 (acres) (rupees) (maunds) (rupees) Jessore Bahular Baor 645 134,138 5,400 162,000 Joydia Baor 535 89,669 4,000 120,000 Habulla RustampurBaor 76 47,030 1,750 56,000 Dacca Narayanganj 18 24,450 1,006 35,210 Bogra Raktadaha Beel 500 83,076 6,600 99,000 Narail Beel and Sakharia Danga 150 43,492 2,700 48,200 Rangpur Bamandanga Beel 70 25,036 1,065 36,000 Kushtia Chand Beel 100 22,700 615 24,600 Ganges-Kobadak Lake 33 15,318 875 26,250 Chandona Doba 70 18,500 516 22,500 Banderdah 180 36,544 850 38,000 Mymensingh Shampur Mora Beel 230 41,235 1,665 49,957 Baleswar- Kutiakuri Beels and Chowka Baor 100 17,844 850 25,500 Diara Nadi 200 41,424 1,650 57,050 Sarbamangal Doba, Betal & Khama Beels 170 26,822 1,400 42,000 Dinajpur Dinajpur 12 1,500 90 3,150 Sylhet Fategang Beel 170 22,680 3,000 36,000 Anduganj Beel 270 36,284 4,200 50,400 Kaibara Fishery 83 14,916 1,600 19,200 Palui Beel 1,700 91,470 9,000 135,000 Aralikona Beel 870 67,284 5,000 75,000 Moraganj Fishery 100 15,966 1,200 21,600 Totals 6,282 917,378 55,032 1,182,617 1 rupee = U.S. $0.21 Net income . Rs 265,239 1 maund = 82 pounds. aSource: Ahmad (1958). 188 The rate of stocking of these waters has not been determined. Population estimation and survey of biota will have to be undertaken for this purpose. However, it will not be necessary to continue stocking after a few years as the fiSh should establish themselves by breeding there. Other important measures that may help to improve the fisheries in such waters are the provision of shelters and fertilization. Very little work has so far been done in Pakistan on this aSpect. The results of work done by Hubbs and Eschmeyer (1938) on the improvement of lakes in Michigan for fishing may be a good basis for experimental work. 5. Fishing and Marketing Dragnets and castnets are not very efficient for fishing in these waters. Gillnets have, however, been found quite suitable. If the fisheries are situated near a city or town- ship, the catch can be sold fresh, otherwise they should be either chilled in ice and transported for sale to a distant market or a portion of them cured. J. Fish Culture in Rice Fields Probably China was the first to start fish culture in rice fields. However, the practice of regular fish cul— ture in rice fields is reported to be on record in Indonesia for the past 100 years (Ahjar, 1955a; Ardiwinata, 1957). 189 Early in the present century, Nicholson (1917) advocated fish culture in the extensive rice fields of Madras, India. In— stances of fish crops from rice fields have since recorded from many rice growing countries of both hemiSpheres. Rice being the staple food of the Pakistanis, rice fields occupy a large share of the arable land. It is nec- essary to keep a certain depth of water in the fields for rice cultivation and since many of them are left fallow for varying periods of time after the crop is harvested, such fields offer conditions well—suited for fish culture. Schuster (1952b) estimates that fish culture is possible in 20 million acres of rice fields in East Pakistan. When fer— tilized and inundated for rice growing, rich biota develop in the water and through fish culture these can be utilized for the production of fish. Simultaneous production of grain and animal protein on the same piece of land is an ideal method of land usage (Schuster, 1955a). Fish culture in rice fields is of great significance in the rural economy of East Pakistan, but little work has been done here by deliberately preparing the fields for stock— ing them with fish. Recently a project ”rich—cum-fish cul- ture" or raising fish with rice at the same time, has been submitted to the Government by the provincial Directorate of Fisheries for consideration (Ahmad, 1956b). In East Pakistan, rice fields are flooded with rain water to a depth of 2-6 feet. Adjoining and connected to the 190 fields are several ponds; besides, there is a system of nar— row canals intended for drainage of surplus water from the fields. During the rainy season, these canals serve as free passage for young fish to the fields. Fishes take shelter in the deeper ponds when the water recedes. Rice is harvested in December, and by January—February, wild fishes like Colisa, Ophicephalus, minnows, Spiny eels, catfishes, climbing perch, and small shrimp are harvested by means of castnets, gillnets and bamboo traps. At present, the production of wild fishes in rice fields of East Pakistan is about 20 pounds per acre. Fish culture in rice fields may be divided into: (1) fish culture as second crop; (2) fish culture between two rice crops; and (3) rice—cum—fish culture. The first form of fish culture is possible in fields where rice is grown once a year, the rest in those where two or more rice crops are grown annually. See further page 195. 1. Water and Soil Conditions A suitable depth of water (at least 10 inches) and fertility of the soil as well as water are necessary for prof— itable fish culture. Rice fields in East Pakistan are usually wet but fish culture is most successful in those fields where controlled irrigation is possible. Fertility of the soil has a great role to play in rice as well as fish production. The cultivator fertilizes the fields before sowing or planting rice. As the field is inun- dated by rain water, some nutrients dissolve in the water and 191 fish food grows rapidly. 21:1 The planktonic organisms in rice fields are similar to those found in shallow ponds and swamps. Mosquitoes find suitable conditions to breed here. Larvivorous fishes feed on the larvae of mosquitoes and other insects. The wild fish fauna are generally predaceous and must be excluded if an extensive fish culture is planned. Field mice live in the embankment during the harvesting season and damage the embankments by boring through them. They also feed on rice in the field. This menace should be minimized by some suitable method like trapping or killing them with poison. Piscivorous birds may also be a menace to cultured fish. They should be scared away by some suitable devices or be shot. 3. Preparing the Field Since a suitable depth of water must be maintained in the field, strong embankments (bundhs) around it will be nec— essary. For fields in which Tilapia is cultured, a height of about 60 cm. is recommended for the bundh to prevent the escape of the fish and the flooding of the field. Vegetables can be grown on wide bundhs. Necessary earth for the bundh will be available by digging a narrow canal around the inner margin of the existing bundh. This canal will serve as a refuge for the fish from solar heat as well as predators. When the water recedes from the field, they will gather in 192 this canal and harvesting will be facilitated. The depth and width of the canal will vary according to the fish cultured; for Tilapia, it may be 75 to 150 cm. (Hora and Pillay, 1962). 4. Stocking Cultivated fish that can (1) thrive well in shallow waters; (2) withstand turbidity due to suSpended clay; (3) tolerate relatively high temperatures and low oxygen tension; and (4) grow to marketable size in a few months are most suit- able for stocking. Common carp (Puntius javanicus), Tilapia melanopleura, gourami, etc. can be grown in East Pakistan's rice fields (Schuster, 1952b). When an association of common carp, Puntia, and Tilapia is planned, 750-1,500 fingerlings per hectare may be stocked (Hora and Pillay, 1962). Hora (1951b) reported that an experiment on rice—cum- fish culture was conducted in Bengal in May, 1945 and, for future reference, its results may be quoted here (Table 25.) From the figures it appears that the profit was as high as 440%, Of the fry stocked, 56,850 were planted in ponds adjoin— ing rice fields, and, according to Hora, the growth of pond fishes was slower than those stocked in the fields. Some fish measured as long as 16 inches in rice fields while the largest fish recovered from the pond was only 11 inches. It was estimated that, taking into consideration the full annual production of the fish stocked in the ponds, the production figure in rice fields might have been as high as 246,000 pounds. 193 TABLE 25. Results of experiment on rice—cum—fish culture in Bengal in 1945a Area of rice fields brought under the project . . . . . . . . . . 691.16 acres Number of carp fry (Catla, rohu and mrigal) stocked . . . . . . . . . 407,100 Size of fry stocked . . . . . . . . . . . 0.75—2.5 inches Cost of fry . . . . . . . . . . . . . . . Rs 4,502.60 Cost of fry transport . . . . . . . . . . Rs 1,124.50 Total number of fish harvested . . . . . 224,158 Range of size of fish recovered . . . . . 5-12 inches Total weight of fish recovered . . . . . 64,452 pounds Value at RS 40 per maund . . . . . . . . RS 31,440 l Rupee = U.S. $0.21; 1 maund = 82 pounds. aSource: Hora (1951b). 194 (358 pounds per acre) at the end of one year. In another rice field, where carps were stocked on the first of September, 1945 and harvested on the 15th of November, 1946, Hora (1951b) found the following rate of growth in them: Species Size of Average growth Average growth stocked fry in length in in length in rice (inch) ponds (inch) fields (inch) Catla 1.7 6.0 7.8 (9.0 largest) Rohu 1.5 5.0 6.2 (7.3 largest) Mrigal 1.4 5.2 6.2 (7.0 largest) He further found that the survival rate was 34% for 93:13, 37% for rohu and 39% for mrigal. This Shows that bottom— living mrigal was somewhat safer from predatory birds even in these shallow waters. Mrigal was found useful in the tilling of rice fields but the best results were obtained when all three Species were stocked together. 5. Management In fields where the depth of water is unsatisfactory, great care must be taken to protect the fish from predatory birds. Excessive growth of filamentous algae should be checked. Regular inspection of bundhs and the water level are also essential. 6. Economic ASPects Advantages.--The advantageous effects of fish culture 195 on rice can be summarized as follows: a. Fish as a second crop: l) The cost of preparing the field for rice cultiva— tion decreases by about 30% (Ardiwinata, 1957). 2) The cost of weeding is lower. 3) The yield of rice increaSes by about 7% (Grist, 1959). b. Fish between two rice crops: 1) 2) 3) The field benefits from longer fertilizing action of the water. Income derived from fish helps to meet the expenses necessary for preparing the field. In case of irrigation, the soil becomes softer and yields better to the plough. c. Rice-cum-fish culture: 1) 2) 3) 4) 5) 6) Water supply is better controlled. Aquatic weeds are better controlled. Movement of fish aerates the soil. Possibly organic substances are better mineral— ized. Disease and pests (stem borer, for example) of rice are more efficiently controlled (Schuster, 1955b). Yield of rice increases by about 15% (Hora, 1951b). Disadvantages.-—Among the disadvantages, the following may be cited: 1) 2) 3) 4) Cost of fish for stocking. Expense of enhanced manuring. Improvement of field embankments. Digging ditches and pits which may reduce yield 196 of rice. 5) Cost of artificial food, if any. 6) Care from predation and disease. 7) Likelihood of rooting out of rice plant by the fish. 8) Keeping water level fairly constant. In irrigated fields, additional water supply eSpe- cially for fish culture may not always be possible. Besides, shallow water in the fields may warm excessively leading to unfavorable conditions. The most opportune time for stocking will have to be determined by repeated and careful experimentation. Plankton production in the field is likely to be maximum soon after flooding. If the fish cannot be introduced at that time, it will become necessary to select such fish as could be advantageously introduced at a later stage. Shallowness and seasonal character of water are peculiar features of this type of fish culture. Conditions are therefore likely to vary with locality. In View of these disadvantages, it becomes essential to: 1) Carry out a well—planned survey of the prevail— ing conditions in different districts of East Pakistan (Figure 7) eSpecially with reference to depth of water, season and its duration, and availability of stocking material. 2) Launch a systematic project of field requirements 197 to elucidate the various problems requiring solution. Without this, large scale utilization of rice fields for fish culture may carry with it the risk of expectations being not fulfilled. The use of inorganic fertilizers, eSpecially ammo— nium sulfate in quantities needful for rice but harmful to the fish, and of calcium cyanamide which is toxic to fish, are adverse factors. Worst of all, however, are the new selective herbicides such as 2,4—D which is poisonous to fish, and the insecticides such as dieldrin and endrin which are fatal to fish even in extreme dilutions. Thus it may appear that fish culture is incompatible with modern agents for weed control as well as controlling insects injurious to rice (Tonolli, 1955; Grist, 1959; Hickling, 1962). .But in view of the desirability of encouraging fish production as a means of improving the diet of the people, it would be a folly also to advocate the use of chemicals particularly in those fields where rice and fish are being raised to— gether. K. Fish Culture in Brackish—water Swamps and Rice Fields The deltaic area of East Pakistan consists of numer- ous islands criss-crossed by a net-work of tidal streams of varying sizes and overgrown in many instances by dense for- ests. This region, known as the Sundarbans (Figure 7), abounds in low swampy lands which are completely inundated 198 during high tides and partially or fully exposed during low tides. By the rapid Silting of creeks, tidal streams, and tributaries of rivers or by the changing of their courses, additional low marshy lands are constantly being formed there. To increase food production and to release pressure on the cultivated lands in this province, reclamation of deltaic area has become necessary. It involves the raising of level of the land and removal of salt content from the soil to make it suitable for rice cultivation. Though the ultimate aim of reclamation is agricultural utilization, raising of fish is intended to be done only during the in- terim period of varying duration. However, in recent years, there is an increasing realization that, in some cases, it is possible and profitable to manage such areas purely as fish culture establishments by constructing and managing ponds. Since the work of reclamation will require large expenditures, it will necessarily be a slow process. Many fields after reclamation on the Indian side of the Sunderbans have been used for rice—cum-fish culture. Hora and Nair (1944), Pillay (1954, 1958), and Pillay and Bose (1957) have made valuable studies on fish cultural practices in these areas . l. Reclamation of Saline Swamps The first step in the reclamation of these swamps 199 will be the construction of a strong, high embankment around the area selected to stop flooding with tidal water. Neces- sary earth for the embankment will be obtained by digging a canal around the site. Its height should be about 30 cm. above the maximum flood level. On the side facing the source of water, a sluice gate is installed in the embankment to regulate the water supply. It is opened during high tide to let the water in, and closed at low tide to stOp the water from draining. The embanked swamp is locally called bheri. Some bheris are quite deep and unfit for rice cultivation and they may be compared with shallow lakes. Tidal water carries sufficient amount of silt and a good part of it settles in the bheri. This gradually raises the level of the swamp thus making it fit for rice transplantation; but the soil of such bheri is salty enough to make it an uneconomic proposi- tion. To remove salt, the bheris will have to be flushed with rain water and the entrance of tidal water checked. 2. Fish Culture during Reclamation Since reclamation of bheris takes 15 to 20 years to complete, the farmer makes some inexpensive arrangements for fish culture in them. These are, besides the main canal all around the embanked area, (1) digging a net-work of smaller canals across the selected swamp for easy drainage, and to give suitable shelter to the cultivated fish, (2) erection 200 of V- or W—shaped bamboo structures in front of the sluice gate to prevent the entrance of undesirable fish or other animals into the bheri. At the apex of the V— or apices of the W, traps are set to capture fish swimming against the current when tidal waters are taken in. The bheri, where fish culture is practiced, is kept closed to tidal water and dewatered from September to January. After January, it is kept open till about September. During this period the following fishes and shrimps of economic im- portance along with many less important Species enter the bheri: Fish-—(l) Gray mullets (Mugil parsia, M. tade, and M3 corsula); (2) Perch (Lates calcarifer); and (3) Nona tengra (Mustus gulio). Shrimp—~(l) Common shrimps (Peneus semi- sulcatus; Metapeneus monoceros; and Leander styliferus). Stocking.--For selective stocking of the bheris, fry or gray mullets are collected from creeks, canals, borrow- pits and estuaries. High tide brings them into the creeks and borrow—pits. At low tide, the narrow creeks are bunded off and, in the case of borrow-pits, the fry are stranded and the fishermen collect them with a large rectangular piece of coarse cloth. The mullet fry are sorted out from those of other Species and shrimps and tranSported in earthen jars like the carp fry. In South India, the mullet fry are conditioned before they are released into the stocking ponds some of which are fresh—water. The collection and acclima— tization of mullet fry are not extensive in East Pakistan 201 but the fish culturist in the coastal districts should be encouraged to start the practice. 3. Ecology of a Typical Bheri There is a marked fluctuation in salinity of water during the period of fish culture, ranging from less than 0.5% in August-November to 31.5% in May (Pillay and Bose, 1957). S23 also Pillay §£_31, (1962). The profuse growth of algae such as Oscillatoria, Lyngbya, Anabaena, Spirogyra, Cladophora, Vaucheria, Euglena and diatoms like Nitzchia and Navicula form an important source of food of the cultivated fish. The only aquatic phanerogamic plants areRuppia Spp. which can withstand salinity up to 60 parts per thousand. The major zooplank— tonic organisms include flagellates, c0pepods, rotifers and nauplii of crustaceans. Gray mullets and shrimps feed on algae. Lates calcarifer, being a carnivore, feeds on small fishes and shrimps. Mystus gulio is an omnivore and feeds on algae as well as small crustaceans. Pillay (1954) conducted experiments on the chemical composition of soil of bheris. His results are shown in Table 26. 4. Capture Fishing starts in October when water is no more taken into the bheri. It is done by means of seines and bam- boo traps ("atols"). Mugil parsia attains a length of 10—15 202 TABLE 26. Chemical analysis of the soil of a typical Bheria Chemical content of soil % Silica and other insoluble matters . . . . 79.47 Iron and aluminum as oxides . . . . . . . . 8.88 Calcium as CaO . . . . . . . . . . . . . . 3.34 PhOSphate as P205 . . . . . . . . . . . . . 1.53 Magnesium as MgO . . . . . . . . . . . . . 1.12 Total nitrogen 0.42 Chlorides 0.137 Sulfates as SO3 0.05 Nitrate nitrogen 0.004 Other 4.849 Total 100.000 aSource: Pillay (1954). 203 cm., M. tade, 22—25 cm., and Lates calcarifer, 12—25 cm. by the end of November; common shrimps (Peneus semisulcatus and Metapeneus monoceros) grow up to 13 and 10 cm. reSpectively. Catches are generally kept in small ponds near the main sluice gate for sale alive. Many farmers transfer small fish into separate rearing ponds and release them again into the bheri during the following January or February. 5. Fish Culture after Reclamation Brackish—water swamps reclaimed for rice culture have the same embankment and canal system which are kept in good condition by the farmers. The harvesting of rice ends by about January, when the field as well as the canals is completely dry. During Spring tides, the young fish enter the canals where they get favorable conditions for their growth because of the shallowness of water and the consequent rich growth of food. With the start of the south-west monsoon in June, the water level goes up in the canals, and the sluice gates are closed against tidal water. The fields are manured with cow-dung and other organic fertilizers and rice is trans- planted. AS the monsoon is intensified, water level goes up in the canals and subsequently the fields are flooded and the fishes gain access to the plots. Excessive water is, of course, drained into the river through the sluice gate at low tides. The monsoon being over by November, the fields 204 begin to dry up and the fishes fall back into the canals and the fishing operations are started. They are caught either by seines or by letting some tidal water in when they swim against the current and are trapped in ”atols" placed in the gaps of the bamboo fencing. The stocking operation in rice fields are rather crude, but the analysis of sample catches from these fields indicates that only 2% of the weight of catch consists of uneconomic species. About 31% consists of Mugil parsia, 14% M. tade, 16% M. corsula and 33% Lates calcarifer; Mustus gulio represents 4% (Pillay and Bose, 1957). Among the shrimps, the more important Species are: Palaemon carcinus, P. rudis, Peneus semisulcatus, Metapeneus monoceros ande, brevipes. Lates calcarifer and the gray mullets show a remark- ably high rate of growth in the brackish-water rice fields. On an average, during the period of culture (September to November), Lates showed 182% increase in length, while Mugil tade and M. parsia 117 and 81% respectively. Lates grows much faster in rice fields than in the bheris or estuaries. The yield of fish is about 150 pounds per acre of rice field without affecting the yield of rice (Pillay and Bose, 1957). Research by Schuster (1952c) shows that Puntius jgvanicus and Tilapia can be reared in brackish-water ponds. He reports that Tilapia eats a certain amount of small shrimps so that it will be an error to stock it in a pond 205 from which a rich crop of shrimp is expected. The general principles of management of brackish-water ponds are similar to those for fresh-water ponds. AS of now, fish culture in brackish—water swamps, rice fields, and ponds either during or after reclamation of land is not very intensive and there is much scope for improvement by way of selective stocking and general improvement of cultural practices. 6. Economic Considerations As already mentioned, fish culture in brackish— waters is only a stage in the reclamation of waste lands for rice cultivation. While during the period of reclama— tion the farmer may not earn anything from the land itself, he may be able to get a substantial income by raising fish for himself and for sale. The construction of embankments, sluice gates, canals, traps, etc. are not very costly. Fry of mullets and shrimps are abundant in the area. The farmer does not wait for some income but begins to earn money Short— ly after the start of the farm by selling mangrove stems as fuel, their bark for tanning nets and hides, by selling skin of lizards and snakes and also by marketing extraneous species of fish caught from the area. Wherever possible, salt making can also be undertaken. In this way, an enter- prizing farmer can start a multipurpose farm in the deltaic area in a profitable way. IV. CONCLUDING REMARKS Although fish culture is practiced as a skilled art, considerable experience and traditional knowledge have gone into the evolution of the techniques. However, proper ex- tension of the practices have been greatly hampered for lack of sufficient knowledge of the basic scientific principles. This has been keenly felt after the independence of Pakistan in 1947. Besides, rapid increase in population in recent years has made it imperative to tap every available resource of food production. To make the necessary technical guid- ance available, agencies like the Food and Agriculture Organ- ization of the United Nations have been organizing training centers and other means of dissemination of scientific know— ledge on the subject of fishery extension services. §g§ further Schuster (l952d), Ahjar (1955b). If the present tempo of development in research and development expressed in the formation of Fishery Development Corporations in both East and West Pakistan continue, it can justifiably be hoped that the industry would advance very rapidly during the com- ing years. Hickling (1961) observed that the greatest of the tropical inland fisheries or the fisheries of the floods, 206 207 will decline in the next 100 years. The human population is increasing too rapidly. The rivers will be trained be- tween embankments and the lands will be settled for inten— sive cultivation. As the wild fisheries decline, the im— portance of fish culture is bound to increase. REFERENCES CITED Adan, R.A. 1935. Le r61e de la chaux en carpiculture. Péche Piscicult. 42, 222-226. Ahjar, M. 1955a. Rice fields-fish culture in Indonesia. FAO Intern. Inland Fisheries Training Center, Bogor, Indonesia. Mimeo Lecture No. 5.64. FAO Rome. 1955b. The inland fisheries extension services in Indonesia. 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Zobairi, A.R.K. 1953. A report on the fisheries of East Bengal, Pakistan. Prog. Fish-Cult., 22(3), 116-120. APPENDIX A COMPREHENSIVE LIST OF FRESH—WATER FOOD FISHES OF PAKISTAN ARRANGED ACCORDING TO THEIR ECONOMIC IMPORTANCE Local name Family Scientific name East West Pakistan Pakistan Cyprinidae Catla catla Hamilton Katla Theila Labeo rohita Hamilton Rohu Rohu Labeo calbasu Hamilton Kalbaus Dhai Labeo nandina Hamilton Nandin na Labeo gonius Hamilton Ghani Seereha Labeo diplostomus Haeckel Kulki—bata Gid Labeo bata Hamilton Bata na Labeo angra Hamilton Kharsa A Labeo boga Hamilton Bagna Bhangan Labeo sindensis Day A Gheri Labeo dyochilus McClelland A Butal Labeo nigripinnis Day A Kali Labeo fimbriatus Bloch A na Cirrhina mrigala Hamilton Mrigal Mrigal Cirrhina reba Hamilton Reba Sunni Crossocheilus latia Hamilton Kala bata Taler garbus tor Hamilton Mahal Mahsir Barbus sarana Hamilton Sarpunti Kharni Barbus SOphore Hamilton‘ Punti na Barbus stigma Cuvier and Val. Punti na Barbus chonchonius Kanchan Hamilton punti na Barbus ticto Hamilton Titapunti na Barbus phutunio Hamilton Phutuni- punti na Barbus puntio Hamilton Bhadipunti na Barbus chola Hamilton Kerrundi A Barbus hexastichus McClelland A Lubar Barbus chagunio Hamilton Jarua na 230 231 Local name Family SCIentific name East West Pakistan Pakistan Cyprinidae ASpidoparia morar Hamilton A Chilwa (continued) Amblypharyngodon mola Hamilton Moa A Amb2ypharyngodon microlepis Bleeker na na Barilius vagra Hamilton Koksa Lohari Barilius bendelinsis Hamilton Joia Chal Barilius barila Hamilton Caedra na Barilius barna Hamilton Bhola na Barilius tileo Hamilton na na Rasbora elonga Hamilton Along na Rasbora daniconius Hamilton Bayi na Esomus danricus Hamilton Dadhikha na Rohtee cotio Hamilton Goonta na Laubuca laubuca Hamilton Dankena na Danio devario Hamilton BanSpata A Danio equipinnatus McClelland Chebli A Danio dangila Hamilton Nipati A Danio rerio Hamilton Anju A Danio chrysops Cuvier and Val. na na Chela gora Hamilton Ghora— Chal chela Chela bacaila Hamilton BanSpati Parranda Chela phulo Hamilton Chela A Garra gotyla Gray A Kurka Garra monti:salsi Hora A na Scaphiodon readingii Hora A na 232 Local name Family Sc1entific name East West Pakistan Pakistan Siluridae Wallago attu Bloch and Schneider Boal Mulee Silonia silondia Hamilton Bacha na Clarias batrachus Linnaeus Magur A Saccobranchus fossilis Hamilton Singhi Singhi Pangasius pangasius Hamilton Pangas na Pseudeutropis garua Hamilton A Bachwa Pseudeutropis murius Hamilton A Pahari Eutrppiichthys vacha Hamilton Bacha Jhalli Callichrous bimaculatus Bloch Kani Pallu Callichrous pabda Hamilton Pabda na Glyptothorax pectinosternum McClelland A Mochi Ailia colia Hamilton BanSpata na Clupisoma murius Hamilton Motusi na ClupiSoma atherinoides Bloch Batasi na Clupisoma garua Hamilton Garua na Mystus aor Hamilton Air na Mystus gulio Hamilton Mystus corsula Hamilton Mystus cavasius Hamilton Mystus tengara Hamilton Mystus vittatus Bloch Nona tengra na Golsa tengra na Kabasi tengra na Bajri tengra na Tengra na Liocassis rama Hamilton na na Arius gggora Hamilton Gagra na 233 Local name Family Scientific name East West Pakistan 7 Pakistan Siluridae Bagarius bagarius Hamilton Bag mach na (continued) Glyptosternum cavia Hamilton Kani tengra na Erethistes hara Hamilton Kula kanti na Clupeidae Hilsa ilisha Hamilton Hilsa Hilsa Gadusia chapra Hamilton Chapila na Corica soborna Hamilton Subarna karika na Raconda russeliana Gray Kura phasa na Engraulis telara Hamilton Teoach na Odficephflidma Ophicephalus marulius Hamilton Gajar Saul Ophicephalus striatus Bloch Shol Saul Ophicephalus punctatus Bloch Taki Daula Ophicephalus barka Hamilton Tila Shol na Ophicephalus gachua Hamilton Gachua Dauli Notopteridae Notopterus notopterus Hamilton Pholi na Notopterus chitala Hamilton Chital Pari Anabatidae Anabas testudineus Bloch Koi na Ambassidae Ambassis baculis Hamilton Phopa chanda na AmbasSiS rangg Hamilton Lal chanda na Ambassis nama Hamilton Chanda na OSphronemidae Colisa fasciata Bloch and , Schneider Khalisa. na Colisa chuna Hamilton Chuna Khafisa na Colisa lalifis Hamilton Lak-khalisa na Nandidae Nandus nandus Hamilton Bheda na Badis badis Hamilton na na 234 Local name Family Sc1entif1c name 'East West Pakistan Pakistan Belonidae Xenentodon cancila Hamilton Kakia na Cichlidae Tilapia mossambica Peters Tilapia Tilapia Mastacembelidae Ma st a cembelus armatus Lacepede Baim Bam Mastacembelus aculeata Bloch Tara baim na Mastacembelus zebrinus Blyth Pankal na Mugilidae Mugil corsula Linnaeus Bata na Mugil tade Forskal Bhangan na Mugil parsia Cuvier and Val. Kachki na Mugil cephalus Linnaeus na na Latidae Lates calcarifer Bloch Koral na Sources: Day (1873, 1958); Khan (1934); Ahmad (1953); Qureshi (1951); and FAO (1961a). Explanation of notations: A na not known to inhabit this province. local name not known. PLATES 236 PLATE I Fresh—water food fishes of Pakistan (Top to bottom) a. Catla catla Hamilton b. Labeo calbasu Hamilton c. Cirrhina mrigala Hamilton d. Barbus tor Hamilton PLATE I 237 238 PLATE II Fresh-water food fishes of Pakistan (continued) (Top to bottom) a. Labeo nandina Hamilton b. Lapeo gonius Hamilton c. Labeo rohita Hamilton d. Lates calcarifer Bloch (also found in brackish-water) 239 PLATE I I 5”” «up... I}... 1's“. 5777413. 3', “0’ H? R“ “9.29m ‘52:... ’22.». 240 PLATE III Fresh-water food fishes of Pakistan (continued) (Top to bottom) a. Ophicephalus marulius Hamilton b. Ophicephalus punctatus Bloch c. Anabas testudineus Bloch d. Wallago attu Bloch and Schneider e. Saccobranchus fossilis Hamilton 241 PLATE I I I \ - m a. ts. ~32 a F‘ . 242 PLATE IV Fresh—water food fishes of Pakistan (continued) (Top to bottom) a. Colisa fasciata Bloch and Schneider b. Ambassis baculis Hamilton c. Notopterus notopterus Hamilton d. Notopterus chitala Hamilton PLATE I V 243 244 PLATE V Fresh—water food fishes of Pakistan (continued) (Top to bottom) a. Clarias batrachus Linnaeus b. Clarias batrachus Linnaeus with labyrinthiform accessory reSpiratory organs exposed c. Tilapia mossambica Peters (male) d. Tilapia mossambica Peters (female) PLATE V “A.“ 246 PLATE VI Fresh to brackish—water food fishes of Pakistan (Top to bottom) a. Mugil corsula Linnaeus b. Mugil parsia Cuv. et Val. c. Hilsa ilisha Hamilton PLATE VI 247 TATE UN WTITIGU‘WIII 1 WI 3 1 293 030 :E ri‘mir'firflwuifillfirfl'“ 7 1 5 01 5