EXPERIMENTS IN ThE HOLDING OF BAIT MINNOWS By BROTHER DONALD ALLEN, 0.5.0. A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Zoology 1952 THESIS Ora-53 ACKNOWLEDGMENTS I wish to express my deep apprecia- tion and gratitude to Dr. Robert C. Ball who suggested and outlined this investi- gation, provided me with the materials necessary for conducting it, and encour- aged its completion with many helpful suggestions. ...~1..> . My! Acknowledgments . . . Introduction. . . . . The Fatnead Minnow. . Holding Minnows . . . Methods and Equipment TABEE OF CONTENTS Results of Holding Investigations Minnows from Fertilized and Unfertilized Tanks. Minnows Held at Varied Stocking Concentrations Minnows Held in Cleaned and Uncleaned Aquaria. Fed and Starved Minnows. Loss among Large and Small Minnows . Discussion. . . . . . Summary . . . . . . . Literature Cited. . . Page ii 10 19 52 41 53 63 69 82 85 87 INTRODUCTION In recent years the rapid decline in the number of minnows used as forage by game fish has become a cause of concern to fishery biologists as well as to fishermen. Deprived of these forage fish the game fish remain under- sized, become stunted, and their numbers become propor- tionately fewer. Schoenfeld (1949) states that 1,800 to 3,000 minnows are required to raise a northern pike to ma- turity and 2,000 are needed to bring a bass to legal size. The increasing fishing preSsure as reflected in the increasing number of fishing licenses being sold each year has become and is continuing to become a more important factor in the shortage of minnows. In order to satisfy the fishermen's demand for bait minnows, bait dealers and fish- ermen themselves have rapidly depleted the supply of minnows in streams, rivers, and lakes where once these fish abounded. There is little if any likelihood of a decrease in the fishing pressure. Foreseeing this situation several of the Midwestern States have placed restrictions on the taking of minnows from public waters. In Missouri a prohibition was placed on the taking of minnows from any of the game fish waters. Minnesota prohibited the taking of minnows from all waters where the game fish populations has been endangered. 1 In order to obviate this difficulty the attention of fishery workers and bait dealers has been directed to the raising of minnows in ponds. Some dealers have long raised their own minnows either in natural or artificial ponds. Minnesota has also placed restrictions on the mesh size of nets used in harvesting the minnows, the type of transportation equipment which may be used in carrying the minnows, the minimum aeration requirements of transporting and holding tanks, and the maximum lead capacities of these tanks. The initiation of these further restrictions on transporting and holding equipment is testimony to the fact that the waste attendant with the handling and holding of minnows is very great. "And it has been estimated that for every minnow sold, five are lost or wasted.” (Schoenfeld 1949). To a large extent the shortage of minnows is due to this waste. It was the purpose of this study to investigate min- now losses in holding tanks with the view of determining their tolerance to conditions normally met with while being held. Specifically, the objectives were to: (1) Observe whether minnows taken from fertil- ized or unfertilized ponds would best survive a period of holding in which food was with- held from them. (2) Determine the maximum stocking capacity of a given container when compressed air is used as a device for aerating the water in the container. (5) Determine the extent to which fish loss- es may be reduced by keeping the holding tank clean. (4) Note the extent feeding reduces the mor- tality of minnows being held. (5) Ascertain whether the size of the minnow has any effect on its ability to survive holding conditions. THE FATHEAD MINNOW As was mentioned before, in recent years because of the shortage of forage and bait minnows attention has been focused on the pond culture of these fish. Minnows con— trary to popular belief are not the smaller members of any species of fish, but are members of the Cyprinidae family. Minnows of eastern and central North America can be dis- tinguished by the following characteristics: the fish have no teeth on their jaws; there are no scales on the head, but scales cover the other parts of the body; except in carp and goldfish.none of them have spiny rays in their fins; except on the carp and goldfish there are lessthan 10 rays in the dorsal fin; the pelvic fins are abdominal in position; the fish are usually small being under six inches in length. Many members of the family are known to be forage fish and frequently used as bait. However, not all of these can be successfully propagated in ponds. Various considerations must be weighed in choosing the species that is to be stocked in a particular pond. Tb be suit- able for raising on a commercial scale, a minnow should have a high reproductive capacity and should spawn in quiet water on aquatic plants or under submerged objects. It should be able to live on minute animals and plants 4 suspended in the water or in organic remains in the bottom mud. It should reach a marketable size in a year, if not sooner, be readily taken by game fish, and be hardy on the hook. The northern fathead minnow, Pimephales promelas promelas (Rafinesque) is a forage fish for it serves as the food of other fish. Many of the workers concerned in the program' of the pond culture of forage and bait min- nows agree that the fathead or blackhead minnow as it is sometimes called would lend itself quite successfully to such a program. The fathead minnow, which was used in all the investigations reported on in this paper, has many de— sirable features which recommend its propagation in ponds. A sketch of the life history of the fathead minnow will suggest the reasons why this species is admirably suited to propagation in fish ponds. . Body'Form The following is a general description of the fathead minnow taken from Dobie, Meehean, and Washburn (1948). First obvious ray of the dorsal fin thick- ened so that it stands out; mouth small, terminal, and upturned; scales small and crowded behind the head; back rounded and arched; lateral line only on the anterior half of the body; breeding male with.b1ack- head; soft swollen pad on top of neck re- gion; breeding tubercules on snout and un- der chin; lining of body cavity black; in- testine two to three times body length. 6 The males are larger than the females and may reach a length of 5% inches. Range Radcliffe (1931) quotes Davis and Wiebe as saying that "the blackhead minnow is a small species with a wide geographical distribution, but is abundant only in cer- tain localities." Hubbs and Lagler (1947) indicate that their range extends from the Prairie Provinces of southern Canada through the southern drainage of Hudson Bay to the Maritime Provinces; south to Maine, the Champlain basin of Vermont and New Ybrk, the Hudson and Susquehanna river systems of New Ybrk, the Ohio Valley in western Pennsyl- vania and New Yerk and the Cumberland system in Tennessee; and to northern Kansas (with an isolated population in northern Oklahoma) and Colorado. The minnow is generally distributed throughout the Great Iakes system. In the northern parts of Michigan and Wisconsin it is found in boggy lakes, ponds, and streams; southward and westward it frequents silty lakes and streams. The minnow according to Radcliffe (1931) prefers still water and a muddy bottom and would be well suited to intensive cultivation in ponds as indicated by experiments conducted at the U. S. Fisheries Station at Fairport, Iowa. Feeding Habits Hubbs (1933) opines that there are certain advantages in the pond culture of fathead minnows. The fish are not predacious on the fry; their mouths are entirely too small to eat them. They are bottom feeders and eat very little plankton and, therefore, are less dangerous than the golden shiners would be. Coyle according to Radcliffe (1951) says that they feed largely on algae, animal food being proportionately less abundant than that derived from plants. They seem to feed indiscriminately on a large number of algae. Coyle concludes by stating that "the algal species found in the alimentary canal of the fat- head depends upon the habitat in which the fish is taken; yet the number and size of the gill rakers of the fish de- termine to a great extent what forms are retained in the alimentary canal." Besides feeding on the microscopic plant food Dobie, Meehean, and Washburn (1948) report that they will take animal plankton and insects. Spawning Moore (1952), and Radcliffe (1931) state that the fat- head minnow has an extended spawning period. In some 10- calities the season extends from May until the latter part of August. Dobie, Meshean, and Washburn (1948) state that, "a temperature of about 64° F. seems necessary before spawn- ing begins." The eggs are deposited on the underside of stones, boards, and other objects. Several females may de- posit their eggs on the same nesting site, the eggs being carefully guarded by one male fish. Wynne-Edwards (1932) 8 noted that the males are very pugnaciousat these times. He continues by saying that, "the males at that time had the rugose skin between the back of the head and the dor- sal fin fully developed." He explains that the male strokes the usually single layer of eggs on this spot. The eggs may be rolled without becoming detached so that the males behavior probably rolls over the egg and permits a free access of oxygen to all sides, this probably being im- portant in Stagnant muddy water. Dobie, Meehean, and Washburn (1949) have observed that: From 36 to 12,000 eggs have been deposited at one site in a circular or oval spot. A single female has yielded 4,144 offspring in 11 weeks, and spawned 12 times. The eggs hatch in 4% to 6 days. In some experimental ponds more than 200,000 fish (528'pounds) have been harvested from a single acre. Growth Rate Embody in a discussion following Hubbs' (1933) paper says, speaking of what fish to use for propagation pur- poses, "and then the question of size comes into it, because the fish which.will produce most economically will be one that is produced in one summers growth." Another advantage of propagating the fathead in ponds is its rapid growth. This is what gives value to the extended spawning season. Schoenfeld (1949) declares that if the blackhead 9 minnows hatch around June 1, they should reach two to four inches by August, and that these first-hatch minnows will spawn during the first summer, and their fry reach 1% inches by September and be of bait size in time for the fall trade. The minnows should be harvested and used for bait after they have spawned for it has been reported that they die soon after that. HOLDING MINNOWS A recognition of some of the problems which con- front those who hold minnows preparatory to their sale will make the investigations reported on in this paper more intelligible. Although all the agents responsible for fish loss were not included in this investigation, most of them are accorded a brief treatment below. Often it is necessary to transport the minnows from where they have been reared and place them in holding tanks. It has already been mentioned that one writer believes that five out of every six minnows harvested are lost or wasted. In addition to the loss and waste of minnows due to the effects of seining, handling, and transporting many minnows die or are lost because of improper methods of holding. Improperly constructed tanks or containers, over- crowding, insufficient oxygen, lack of cleanliness, water that is not suitable for fish life, and too rapid changes in the temperature of the water are some of the causes of the loss of minnows in holding tanks. Fungus and other pathological conditions are usually the result of unfavorable conditions prevailing in the holding tank. Adherence to the suggestions indicated below will eliminate most of the loss commonly occuring in tanks. 10 11 Tanks It is desirable to hold the minnows in a number of small tanks rather than in one large one. Small containers are more easily managed, and outbreaks of fungus and other diseases are more easily brought under control. The tanks should be of such size that all the fish.in them are sold within four to six days. Before any other minnows are placed in the tank the container should be drained, cleaned, and thoroughly sterilized in sodium hypochlerite. The sides and bottom of the tank should be scrubbed with a solution of one-half pint of any of the common household bleaches in 15 gallons of water. The container needs to be rinsed until all traces of the bleach are gone. Each tank should operate independently of the others; one tank should not drain through another. The tanks should be smooth.on the inside to prevent the fish from losing their scales when rubbing their bodies on the sides or bottom.of the container. They should be deep enough so that the fish are not injured by the devices used in aerating the water. If the tanks are constructed of wood or smooth concrete they must be seasoned before minnows are placed in them. The containers may be seasoned by filling them with water and keeping them filled for two or three weeks, changing the water two or three times during this period. Seasoned tanks are preferable to tanks painted with asphaltum. 12 Seasoning removes many of the harmful chemicals which wash out of the wood or concrete into the water. Water Supply If at all possible the holding tanks should be con- stantly supplied with pure, cold water. The cooler the water the more oxygen it holds, and therefore, the greater the number of minnows that can be held in the container. It is preferable to keep the temperature of the water below 50° F. Spring water is ideal for it is both cool and pure. Tap water that contains chlorine should not be used unless the chlorine has been removed. A charcoal filter will re- move chlorine. According to Stoye (1955) fresh tap water destroys the protective mucous covering which envelope the entire fish. The fish in this condition are much more sus- ceptible to fungus attacks. Dobie, Meehean, and Washburn (1948) recommend that water should enter the tank through pressure jets at a point well above the surface of the water. An overflow pipe must be provided and this should be placed at or near the bottom of the container. This will aid in the removal of stagnant water and solid wastes. Aeration Regardless of what device is used in aerating water it should be of such nature as to maintain a minimum.of 15 three parts of oxygen per million parts of water at all times. Adding the water to the tank through pressure jets placed well above the surface of the water will keep the oxygen content of the water up. Small pumps and compressors are very useful in aerating the water. The air should be released through carborundum tips or through perforated oxygen release tubes. When fish rise to the surface and try to obtain oxygen from the air above the water it is a sign that the oxygen content of the water is dangerously low. This is not to be regarded as an infallible guide for many times the water may be lacking the proper amount of oxygen and the fish may fail to rise to the surface. Feeding greatly increases the consumption of oxygen. In an investigation Davis (1947) found that in a trough con- taining 1,500 brook trout having an average weight of 15.4 grams, the oxygen consumption before feeding in the morning was 5.07 parts of oxygen per million parts of water or 29.65 percent of the total amount of oxygen present. After having been fed on 500 grams of food the consumption of oxygen rose to 7.26 p.p.m. or 70.08 percent of the total amount of oxygen present. Several hours later the consumption was 4.72 p.p.m. or 55.84 percent. After a second feeding that day the consumption rose to 8.55 p.p.m. or 81.4 percent of the 14 total amount of oxygen present. It is evident from the foregoing results that in over- crowded troughs the oxygen content of the water may fall to dangerously low levels during or shortly after feeding, al- though at other times the oxygen content may be more than sufficient for the needs of the fish. (Davis 1946) Temperature Changes When fish are subjected to sudden temperature changes of more than 10° F. they very often receive a fatal shock. The effects may not become immediately apparent. They may die several hours or even a day later. A twenty minute acclimatization period should be allowed for every 10 de-' gree difference in water temperature. Floating or placing the receptacle containing the fish in the tank the fish are to be placed in later until the temperature of both recep- tacle and tank are alike is one method of tempering the water slowly. Feeding If the fish are to be sold within a week they do not need to be fed, but for any longer periods they will need to be fed. Dobie, Meehean, and Washburn (1948) remark that . in a series of experiments conducted by the Wisconsin Fish Management Division on the effect food has on the loss of minnows in holding tanks, it was noted that at a tempera- ture of 46° F. starved brassy minnows succumbed to heavy 15 infestations of fungus. This was not true for minnows re- ceiving a full diet of canned carp. Brassy minnows fed only half as much survived almost equally as well, showing only a slightly greater weight loss. Minnows will take a variety of foods. Foods that are attractive and readily taken by the minnows and which are easily handled and convenient to store should be chosen. The minnows need to be fed but once a day and only as much as they are able to clean up in 15 mdnutes. All uneaten food should be removed after this period for such food rapidly pollutes the water in the container. Fathead min- nows have small mouths so the food they receive must be small. Brassy minnows because of their larger mouths are able to take larger food. live food such as mealworms and earthworms make ex- cellent food, but they must be small enough or out fine enough to be easily taken by the minnows. Because live foods are seldom present in sufficient quantities and be- cause they are not as easily handled as dry foods most bait dealers rely on dry food for feeding their minnows. Various workers, Dobie, Meehean, Washburn (1948) and Dobie (1948) state that oatmeal makes a satisfactory food. Other foods such as soybean meal and cottonseed meal are also advocated. It was found that ground dog ration pellets make excellent fish food. This food is taken readily. It is a more balanced food than the dry foods l6 mentioned above for in addition to containing most of these meals it contains needed vitamins and minerals. Diseases It is easier to prevent outbreaks of diseases than to cure them. Proper care and handling of the minnows greatly reduces the possibility of infection by diseases. A dip net should always be used in removing minnows from tanks. The longer minnows are held the more susceptible they become to attacks of disease. Fungus is the most common disease affecting minnows in holding tanks, and more destructive to these minnows than all the other diseases and parasites. The minnows are less affected by tail rot. Fungus first occurs as tuft-like threads approxi- mately 1/5 of an inch long radiating from the body of the fish. The disease spreads over the body of the fish quite rapidly and the minnows may later appear to be enveloped in a fuzz or cotton—like growth. The color of the fungus is dull white, but if the water is roiled the color may appear to be brown or dirty gray. Epidemics of fungus among healthy fish do not often occur. Davis (1947) speaking of trout, although the state- ment holds equally as well for minnows, says that: Any physical injury or infection by external parasites may enable 17 this fungus to obtain a foot- hold on the fish and then to spread from the original site of infection. Susceptibility to infection is greatly in- creased if the fish are suffer- ing from general debility or are living under unfavorable conditions. If an epidemic of fungus occurs the dead and dying fish should be removed and destroyed. All dead fish whether or not they are already infected with fungus should be reb moved for they become breeding grounds for fungus and may, consequently, aid in its spread. The remaining fish should be dipped in a 1:15,000 malachite green solution (approxi- mately one-eighth ounce of malachite green in 15 gallons of water) for 10 seconds. The tank should be drained and sterilized with a l:l0,000 solution of sodium hypochlorite (one-half cup of any of the common household bleaches in 15 gallons of water). All the tools and nets need to be sterilized for several hours in the same solution. The tools and nets should be sterilized daily until the epidemic is over. Tail rot which is also known as fin rot is believed to be due to a rod-shaped bacterium. The infection normally starts on the peripheral portions of the fins and appears as a white line along the edge of the infected fin. The lines become wider as the bacteria work their way to the base of the fin. The outer portions of the fin take on a 18 appearance. It sometimes happens that the whole fin drops off before the outer margins of the fin become frayed. For minnows, overcrowding is probably as important a factor in the appearance of tail rot as it is for trout. Frayed fins do not necessarily indicate fin rot. Frayed fins may appear as a result of injury. The infected minnows may be given the treatment noted above for fungus infections. Another treatment advocated by Davis (1947) consists in dipping the minnows in a l to 2,000 copper sulfate solution for one or two minutes. The treat- ment will need to be repeated several times during a 24 hour period if it is to be effective. The treatment must be ap- plied in the early stages of the disease otherwise the min- nows already infected will fail to respond and will die. Schoenfeld (1949) remarks that, "Some dealers dip min- nows in a mercurochrome solution (two tablespoonsful of mer- curochrome to a gallon of water) before putting them in a bucket to prevent fungus and tail rot." LEE THODS AN D EQU IPMEN T Fish and Pond Facilities Fathead minnows, Pimephales promelas promelas (Rafinesque), obtained from the Wolf Lake State Fish Hatchery, in Michigan, were used in all the investiga— tions described in this paper. The minnows were har- vested from Ponds 4 and 5 on September 8, 1949. Ponds 4 and 5 have a surface area of 1.0 acres and a maximum depth of approximately 7 feet. The bottom.soil of the two ponds are similar; both are sandy clay bottoms. A large spring supplies both ponds with water. Both ponds were stocked with adult fatheads in the spring and the yield harvested in the fall. Pond Treatment .A.10-6-4 commercial inorganic fertilizer containing 10 percent nitrogen, 6 percent available phospheric acid, and 4 percent potash were applied at three week intervals throughout a period extending from June 1 to August 24. Pond 5 was not fertilized. The effect of fertilization was reflected in the bottom vegetation. Pond 4 had no bottom vegetation, but Pond 5 had a growth consisting mainly of Chara. Preliminary Holding After being harvested on the 8th of September the 19 20 minnows were held for two days in a large holding tank at the hatchery. On September 10, 1949, approximately 100,- 000 of these fish were transported to East lensing, Michi- gan, 81 miles away, with very little loss. Until the in- vestigations began, the fish were held in a 1,500 gallon concrete tank which was partitioned into four equal com- partments. The mortality during this preliminary holding period was very high. One-half of the fish died in the first few days of holding. In the stock tank quite a few of the minnows at the point of death swam or moved with a spiral motion. In aquaria used in the investigations where the minnows were starved, the minnows on the verge of death swam.weakly near the surface with their head up and caudal fin down or swam with a spiral motion or off balance near the bottom of the tank. The concrete tank although seasoned prior to the in- troduction of minnows may not have been thoroughly washed. Chemicals may have washed out subsequent to the seasoning and may have been responsible for part of the minnow loss. A great many of the fish that died in the stock tank appeared to have hemorrhaged in certain areas of the body for these areas were very red colored. The area around the head and gills was especially affected, the anal region slightly less so. This condition seemed to occur in cycles coinciding to the period when water was being run into the 21 tank. The water flowing into the stock tank contained chlorine, the amount varying from time to time. At times the chlorine content of the water was known to be quite high. Chlorine in large amounts of water destroys the protec- tive mucous covering of the fish. This in turn renders the fish more susceptible to attacks of fungus and other di- seases and parasites. Fungus growths were noticed on the body of a number of living and dead fish. The chlorine contained in the water is thought to have caused the greater part of the large number of minnow losses. The cause of the hemorrhaging is not definitely known. It might have been indirectly caused by the presence of chlorine in the water. After the protective covering of the minnows had been removed by the chlorine any organisms come ing in contact with the skin may have irritated the fish to such an extent that they tried to remove the irritating or- ganisms by rubbing the infected parts on the cement sides of the tank. Continuous rubbing may have resulted in hemor- rhaging at these areas. The large loss of minnows in the stock tank was the result of the combined ill effects of harvesting, trans- porting, and holding. Laboratory Procedure The investigations were carried out by comparing the loss of minnows when the fish were subjected to various 22 sets of conditions which affected their holding ability. An example of this is illustrated in the investigation which was carried out as follows: four aquaria were stocked with minnows, and in all of these aquaria the holding conditions to which the minnows were subjected to were the same, except that the minnows in two of the a- quaria were fed while in the other two aquaria food was withheld from the fish. The holding ability of the minnows was noted by comparing the loss of minnows when the fish were fed, with the loss sustained when food was withheld from the minnows. The investigation of the other factors affecting the loss of minnows in holding tanks was carried out in a similar manner. Only one variable was considered at any one time. Table 1 explains the procedure followed in each of the 12 tanks in order to determine the effect of these factors. Table 2 lists the weekly loss of minnows in each of the tanks. The minnows used in the investigations were held in 12 aquaria having glass sides and stone ends and bottoms. Each aquarium had a length of 29-1/2 inches, a width of 15-5/4 inches, and a depth of 16 inches. The surface area of each was 465 square inches and the capacity was approx- imately 52 gallons. A continuous supply of compressed air from a central source was used in aerating the water of the aquaria. 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A. an an .3. on 3 on 8 ma b» can and who u on vn a HH on no on «c an v» 3 9. on 2. do» a on «A .3 on oh—Wmh o E v x n m .n nofiu‘l BE eflmqmwm . Snip ‘ H can 3H... 4.3%me Easeme- , A 27 The air was released into the tanks through cylindrical carborundum tips. Dead fish were removed once or twice daily from all aquaria except Tank 11. Excrement and excess food were daily siphoned from the bottom of all tanks except Tanks 6, 8, and 11. Not more than 10 percent of the volume of water was removed from any of the tanks at any one time. The water removed through siphoning was replaced with seasoned water of the same temperature. The water temperatures of all tanks were taken daily in order to determine whether the water temperatures of any of the aquaria varied sufficiently to affect the holding ability of minnows stocked in the aquaria. The maximum.variation in the water temperature of any two of the aquaria did not exceed 2° C.; the variation tended to remain within .5° C. This variation was thought to be too small to create a difference in the holding ability of minnows stocked in various tanks. The average water tem- perature in all of the 12 aquaria was 20° C. The standard deviation was less than 2° C. The temperature of the water in the tanks during the holding period varied between 12 and 25° C. On only one occasion did the temperature of the water in any of the tanks drop below 16° C. All minnows dying within a two day period following their transfer were not included in the mortality counts. 28 By following this procedure most of the minnows that might possibly have been fatally injured by their transfer would have died and further minnow losses would have been little affected by the transfer. After the two days minnow losses could be attributed to the conditions existing in the aquaria. During the first and second day after the minnows had been placed in the aquaria, some of the dead fish were noticed with growths on fungus on their bodies. Fish receiving food were fed twice daily on a diet of dog ration pellets ground to a size adaptable for use as minnow food. The pellets contained a minimum protein con- tent of 50 percent, a minimum fat content of 5 percent, a maximum fibre content of 4.50 percent, a minimum carbo- hydrate content of 47 percent, and a minimum content of 42.5 percent of nitrogen free extract. The pellets proved very satisfactory. The minnows took the food eagerly. After a brief orientation period the minnows would approach the water surface as a group when the food was being placed in the tank. Figure 1 illustrates their behavior at these times. The figure also illustrates the aquaria used in holding the minnows. The pellets were found to be more satisfactory than a commercial brand of canned dog food in meat form. This latter food was tried for a week, but it proved unsatis- factory. The dry food form of the pellets facilitated handling and preservation; more care had to be taken of the meat. The undigestible, stringy portions of the manages HmoHpCooH NH on» we who ca pom mafion maoddafi umonpmm .H oastm 50 canned meat not eaten by the minnows as well as the tendency of some of the food to dissolve in the water caused the water to become cloudy and tended to pollute it. Before the minnows were fed the food was weighed and then placed in dishes of the type shown in Figure 1. Water was added to the dishes, the contents stirred, and the finer food particles unlikely to be taken by the minnows removed. This prevented the water from becoming polluted. The dishes were then placed on the bottom of the various aquaria. Ap- proximately 85-90 percent of the weighed food was taken by the minnows. The minnows were stocked in the aquaria on the basis of weight rather than on numbers, in order to insure more uniformity in the rates of oxygen consumption by the minnows held in the various aquaria. The consumption of oxygen by fish depends in part on the size of the fish. A smaller fish consumes less oxygen than a larger one. Since there was a great variation in the size of minnows held in the large cement tank, stocking on a numbers basis may have resulted in two tanks containing the same number of min- nows, but one aquarium containing minnows of substantially larger size. The amount of oxygen consumed in the two tanks might then have been quite different. Observations of the minnows held in Thnks 1 through 51 8 were conducted throughout a period of 84 days, from September 22 to December 15, 1949. Fathead minnows held in Thnks 9, 10, 11, and 12 were observed for 54 days, from October 22 to December 15, 1949. RESULTS OF HOLDING INVESTIGATIONS Comparisons of the Holding Ability of Fathead Minnows from a Fertilized Pond with Those from ‘ an Unfertilized Pond In order to determine whether fathead minnows taken from fertilized ponds withstand holding periods during which they are starved better than minnows taken from.un- fertilized ponds two comparisons were made. The compar- isons involved contrasts in the stocking ratio. Two aquaria, 5 and 4, were initially stocked with 250 grams of minnows (seven to eight minnows per gallon). Tank 5 was stocked with minnows harvested from the fertilized pond (Pond 4) while Tank 4 was stocked with minnows taken from.the unfertilized pond (Pond 5). TWO other aquaria, l and 2, were stocked with 500 grams of minnows (15-16 minnows per gallon). Thnk 1 was stocked with minnows from the fertilized pond and Tank 2 with minnows from the unfertilized pond. The minnows received no food. The waste products of the minnows and the dead minnows were removed daily. Minnows Stocked at a Concentration of 250 Grams During the first three weeks of holding the fish from.the fertilized pond suffered fewer losses than did 52 55 the fish from the unfertilized pond. For the three week period the losses among the latter group of minnows al- most doubled those of the first group. During the fourth week the mdnnow losses were low in both tanks; six min- nows from the fertilized pond died as contrasted with only four from the other pond. From the beginning of the fifth week until the beginning of the eighth week, the losses among the fish from Pond 5 (unfertilized) were again no- ticeably higher than among the fish from Pond 4, being 42 in the first case and 70 in the second. From.the eighth to the beginning of the twelfth week the trend was re- versed. The losses among the minnows from the fertilized pond were higher during this period. As the holding period increased more of the minnows from the fertilized pond died in comparison with the min- nows from the unfertilized pond. For the four week period the losses were 118 and 71 respectively. The losses dur- ing the last week were identical being eight in both cases. By the end of the fifth week, as pointed out in Figure 2, 25 percent of the minnows from the fertilized pond had died. By the end of the eighth week 50 percent had died and by the end of the tenth week 75 percent of the original number had died. In the case of the minnows from the un- fertilized pond these percentages were reached by the end of the second, sixth, and eighth weeks respectively. At 54 the end of the 12th week 2.2 percent of the original stock of 255 minnows from.the fertilized pond remained. Among the minnows from the unfertilized pond 4.2 percent of the original 555 mdnnows were still alive when the investiga- tions were concluded after the 12th week. The minnows from Pond 4 seemed to be able to with- stand holding more successfully for the first six weeks than the minnows from Pond 5. The higher mortality figures among the minnows from Pond 4 during the 8th, 9th, 10th, and llth weeks as compared with minnows from Pond 5 may partly be attributed to their greater numbers at these times. If the minnows from Pond 4 held better during the first seven weeks they did not seem to do so in the last weeks of the investigation. In the latter period the fish from both ponds held equally as well. Minnows Stocked at a Concentration of 500 Grams The most striking difference in the mortality of min- nows from the two dissimilar ponds when stocked at a con- centration of 500 grams as indicated in Figure 5 was noticed in the first week of holding. During this week 105 minnows from the unfertilized pond died as contrasted with only 58 from the fertilized pond. After the first week and for the balance of the in- .60.“ pod who: mecca—HE one .maodcaa mo madam 0mm spas momOOpm mmcmp 03» dd hpaamphoz .m onswam lunm—ibuflq .J ._ .7 .. In." H dufuwfltm Lilo 56 . QOHNMQ 830m NH 3 an HH OH 0 m b o a u. n a H T 4 q 4 a) q q 4 1 1 1 J 57 vestigation, the losses among the fish from the unfertil- ized pond tended to be slightly lower than the losses among the fish from the fertilized pond. As indicated in Figure 5 by the end of the fourth week 25 percent of the fathead minnows from Pond 4 had died, by the end of the seventh week 50 percent had died, and by the end of the eighth week 75 percent had died. Similar per- centages among the fathead minnows from Pond 5 were reached by the end of the first, sixth, and eighth weeks respective- ly. At the conclusion of the investigation 5.9 percent of the 591 minnows from the fertilized pond remained while 5.8 percent of the minnows from the unfertilized pond con- tinued to live. The minnows from the fertilized pond appeared to be in better condition during the holding period than the min- nows from the unfertilized pond. It may be noted from the foregoing results that among fathead minnows taken from a fertilized pond and from one not fertilized and the minnows subsequently held and starved, the loss among the fish from the former pond was less than the loss among the fish from.the latter pond during the first week. The differences are rather large. After the second week the results obtained from holding the minnows at various concentrations indicate that there is little variation in the losses among the minnows from Ponds 4‘ .Uom nod one? mBohdHE one .msocdaa mo madam oom Spas moxoopm mxcmp 03» da hpdamuaoz .n oaswam 59 Dough GER—Hon IH a OH 0 m b 0 . o v n u n 8 :45 8.8 gfiug lull. 3E3: one» game.— IIIII \l 40 and 5. If a comparison is made of the mortalities during the two day waiting period it becomes evident that at both the 250 and 500 gram stocking concentrations, the losses among the fish from Pond 4 were much lower than the losses among the fish from Pond 5. At the lighter concentration the loss amounted to 26 among the fish from the former pond and to 95 among the fish from the latter pond. At the heavier concentration the losses were 78 and 158 respectively. The above results offer evidences for the belief that fathead minnows from a fertilized pond are better able to withstand the ill effects of handling and holding during the first week or ten days than fathead minnows harvested from.ponds not fertilized. After the first week or 10 days the holding ability of fathead minnows from ferti- lized and unfertilized ponds is about the same. Comparisons of the Holding Ability of Fathead Minnows When Stocked at Various Concentrations_ In trying to determine the effect various concentra- tions of minnows have on the ability of minnows to sur- vive holding periods when starved, several comparisons were made. One comparison was made between the fish taken from a fertilized pond and stocked at a concentration of 250 grams or eight minnows per gallon and fish from the same pond but stocked at a concentration of 500 grams or 18 minnows per gallon. Another comparison was made be- tween minnows taken from an unfertilized pond and stocked at concentrations of 250 grams or 11 minnows per gallon and 500 grams or 19 minnows per gallon. Observations were also made on minnows from Pond 4 stocked at a concentra- tion of 1,000 grams or 55-56 minnows per gallon. The fish at this latter concentration were fed. The dead fish and the waste products were removed from all tanks. The average water temperatures in all of the 5 aquaria was 20° C., the standard deviation lying within 2° C. The temperature of the water in the tanks during the holding period varied between 12 and 25° C., but only on one oc- casion did the temperature of the water in any of the tanks drop below 16° C. The maximum variation in the water temperatures of any two of the aquaria did not exceed 2° C.; the variation tended to remain within .5° C. 41 42 Comparisons between Minnows from the Fertilized Pond Stocked at Concentrations of 250 and 500 Grams During the first week of holding the mortality of minnows stocked at the higher concentration was propor- tionately lower than the mortality of minnows stocked at the lower concentration, the figures being 7 percent and 15 percent respectively. These mortality percentages were calculated by dividing the number of fish in an aquarium at the beginning of a particular week by the number of minnows that died in that aquarium during the same week. Following this procedure comparisons could be made of the mortality among minnows stocked at differ- ent concentrations. After the first week and until the 10th.week the minnows at the lesser concentration suffered fewer losses. The mortality among the fish held at the higher level was proportionately much higher. During the 10th week the losses among the more lightly stocked minnows was con- siderably higher than among the heavier stocked minnows. After the 10th week the losses among the fish still surviving in both aquaria were high. This was to be ex- pected since all the fish were being starved. The loss was slightly higher among the more lightly stocked minnows. An inspection of Figure 4 reveals that at the end of the fourth week 25 percent of the minnows stocked at a 45 level of 500 grams had died, by the end of the seventh week 50 percent had died, and by the end of the eighth week 75 percent had died. Similar percentages were reached among minnows stocked at the 250 gram level by the end of the 5th, 8th, and lOth weeks respectively. Among the former group of minnows 5.9 percent of the fish survived the 12 week holding period. Among the minnows in the latter group 2.2 percent survived the same holding period. Comparisons between Minnows from the Unfortilized Pond When Stocked at Concentrations of 250 and 500 Grams The mortality among the minnows in the two aquaria stocked at the two different levels was proportionately the same in the first week of the holding period. During the next five weeks the loss in the more lightly stocked tank was slightly higher proportionately than the loss in the heavier stocked tank. An exception occurred in the fourth.week. The variation in the losses in the fourth week was slight. The fish stocked in greater numbers sus- tained proportionately mummlhigher losses in the seventh, eighth and ninth weeks than did the fish stocked in lesser numbers. During the 10th and 11th weeks the losses among the two groups of minnows were preportionately similar.- Although the losses among the two groups of fish were .60.“ non one; msocsae och. é whom Eon.“ macaque .Ho hpaawpaoa .w ohdwam 45 QOHmEm Gan—Jon IH fig 0 b 0 a v n a H . 1d n 1 d d 303cm .3.— .m m V grandad no .u can III..- 30.31» h..— .n 0.: whens.- uo .m can Illll L E. \l 46 numerically similar in the 12th and final week of the holding period, the losses were proportionately quite different. In the aquarium stocked with 250 grams of min- nows eight fish died, and in the aquarium stocked with 500 grams of minnows seven fish died. The proportionate varia- tion was of little consequence since the number of fish surviving in both tanks was quite small. As indicated in Figure 5 by the end of the second week 25 percent of the fathead minnows stocked at the lighter concentration had died, 50 percent had died by the end of the sixth week, 75 percent by the end of the eighth.week, and at the conclusion of the investigation that extended over a period of 12 weeks 4.2 of the original number of minnows were still living. In the case of the minnows stocked at the higher concentration 25 percent of the min- nows had died by the end of the second week, 50 percent by the end of the sixth week, and 75 percent by the end of the eighth week. At the conclusion of the 12 week period 3.8 percent of the minnows were still alive. After the fourth week of the holding period it seemed apparent that among minnows harvested from.the unfertilized pond, the loss of minnows in the more lightly stocked tanks was not any lower proportionately than the loss of minnows in the more heavily stocked tank. After the first week the opposite was true among the minnows taken from the fer- .vom pom one: macadaa 035 .m ocom Scum agendas ho hpaaspuoz .m ehdmflm 48 OOHmmm 0530m— IH ma NH Ha OH 0 m b . o n v n N H illlfi q salt 1 + q q 4 u 4 J A 23ng wen .u m V spousal no .m can lullnl «define» hon .m a: cicadas no .u can lullll. on as. 49 tilized pond and held at the same concentrations, the fish stocked at the lighter level holding better. Mortality among Minnows Stocked at a Concentration of 1,000 Grams The conflicting results of the last two investigations were indications that the minnows in both of the more heav- ily stocked tanks had not been overcrowded and that probably more minnows could be held in both of the tanks without proportionately greater fish losses. It was decided to stock an aquarium with 1,000 grams of minnows. This amount- ed to 35-56 minnows per gallon. On October 19, 1,140 min- nows taken from the fertilized pond and weighing 1,000 grams were placed in Thnk 12, containing 52 gallons of water. These minnows had been held in one of the four compartments of the large cement tank before they were placed in Tank 12. They were fed both before and after they had been placed in Tank 12. Except for having received food in the aquarium the fish were subjected to the same conditions as the minnows in all the aquaria mentioned above. The loss in this tank was very heavy throughout the entire holding period. Figure 6 indicates that by the end of the first week of holding over 25 percent of the fish had died, nearly 50 percent had died by the end of the second week, and close to 75 percent had died by the end of the third week of the holding period. 50 The minnows in this tank did not feel well. They fed much poorer than did the minnows which were fed in other aquaria. They were noticed to be in poor shape, being quite emaciated. At a concentration of 1,000 grams the minnows were definitely overcrowded. At the 500 gram level they did not seem to be overcrowded. The point at which the loss of min- nows begins to increase proportionately lies between these two levels. .ooM one: msoddda one .w ocom Scam agendas Ho macaw ooo.a spas noxoopu NH meme 2“ hpaaspaog .o onnmam GOHmMm oaaom 3H a m s. o n d 4 fi - HHHA dame! ma mb Minnow Losses as Affected by Cleaned and Uncleaned Holding Tanks The investigations reported on in this section were made on minnows taken from Pond 4. Tanks 5, 6, 7, and 8 were stocked with 250 grams of these minnows, an average of approximately 9-11 minnows per gallon. All the fish were fed twice daily. In Tanks 5 and 7 allcbad fish and the waste products of the minnows were removed daily. In Thnks 6 and 8 the waste products were allowed to col- lect, but the dead fish.were removed every day. The aim of the work here was directed towards determining the effect that accumulated waste products have on the loss of minnows held in small tanks. Figure 7 points out that the loss of minnows held in the aquaria which were cleaned was lower than the loss of minnows in the other two aquaria which were not cleaned. During the first week of the holding period, although not much wastes had collected in the uncleaned aquaria, the combined losses of minnows in Tanks 5 and 7 were less than the combined losses on minnows in Tanks 6 and 8. During the second week a very high loss was sustained by the minnows held in Thnk 8, one of the aquaria which were not cleaned. Over one-third of the original number of min— npws died. Out of the 131 fathead minnows that died during that week, 112 died in a single evening. In the two days 53 .manmsvm vocmoaods was vmdmoao CH msoddaa so mmoq .b ohswfih 55 OOHMMQ OKHQAOm zH mMMHI C. 5.: ago coco. o 3 may. go Salt! 4 S 523 go HBHAaa macadaa Ho uaoohom .m onswam 62 “a 5 8 1‘ VlIlIlllIlll . ”Illlllllll A 505 Prose—nu Edi g muHh a lump Effects of Starvation on the Mortality of Fathead Minnows In determining the extent to which starvation af- fects the mortality of minnows in holding tanks compar- isons were made between fathead minnows in each of three aquaria stocked with 250 grams of the fish, an average of approximately eight to nine minnows per gallon. All the aquaria were cleaned. The only difference in the conditions under which the fish were held was in the withholding of food from minnows in Thnk 3. The minnows held in Tanks 5 and 7 were fed twice daily. The difference in the number of deaths between the minnows being starved and the ones being fed became more pronounced the longer the fish were held. Figure 9 points to this conclusion. In the first four weeks the loss among minnows being starved was light. The mortality among minnows held in Tank 3 was only a little greater than the loss among the minnows held in Tank 5. After the fourth week the increment in the loss of fish held in Thnk 3 became greater as the investigation neared its conclu- sion. During the first five weeks the loss of minnows stocked in Tank 7 was greater than the loss among minnows being starved. The loss in Tank 7 was considerably great- er than the loss in Thnk 5 throughout the first seven weeks; thereafter the losses were similar. 63 .8 Guam Scam doxsp msoddaa no madam 0mm Spa; Uskooum one: macs» one .Aodaa coppovv a was .Aocaa someway m Agenda caaomv n exams ca agendas no hpaasunoz .m oasmHm 65 GOHMMm czHqum aH mMMMB gm 8H» llll 00 0h cod 66 The holding conditions in Tanks 5 and 7 were intended to be identical. As mentioned above the constriction in the rubber tube through which the compressed air used in aerating the water in the aquaria passed was thought to have caused the large loss of minnows in Thnk 7. At the beginning of the fifth week 75 percent of the original number of fish placed in Tank 3 were still living. At the beginning of the eighth.week 57 percent of the fish still survived, but by the end of the same week only 43 percent of the minnows were still living. By the end of the 10th week less than 25 percent were living. Eight min- nows representing 2.2 percent of the original number of fish survived the 12 week holding period. Among the fathead minnows held in Tanks 5, 25 percent had died by the end of the sixth week. After 12 weeks 179 of them.were still living. This represented 64 percent of the total number stocked in the aquarium. By the end of the fifth.week 25 percent of the minnows originally placed in Tank 7 had died. At the end of the twelfth.week 157 fish or nearly 57 percent were still alive. The results of this investigation indicate that at this stocking concentration, withholding food from minnows for three or four weeks will cause, if at all, only a slight increase in the loss of minnows. Whether this would have been true had the fathead minnows been held in greater 67 numbers than was done here is not known. The decline in the strength of starved minnows was quite noticeable. After the first few weeks of holding they could or would not fight the current set up by the air being released in the aquaria. By the fifth week almost all the fish that were starved were noticed to be in poor condition. The minnows receiving food were in much better shape, were much more active, and took food more eagerly. These appeared to hold their own in weight and condition. The larger minnows which were fed would have made good bait minnows. The minnows being fed schooled much more than starved fish. Among the ones that were fed the smaller fish had difficulty in compet- ing with the larger minnows for food. They would feed after the larger fish had become satisfied. In the seventh week a brief examination was made on the minnows that had been receiving food but had died during the week. Judging from outward appearances the fish were in good physical shape. They did not appear thin. The stomachs of these fish appeared full, but were very soft and were easily compressed by the slightest pressure applied to fiais region. Upon examination the body cavity of a large man- npw that had died in Tank 12 was found to contain a large amount of a watery fluid. This fish had looked to be in good condition, but in the region of the body cavity it 68 was quite soft. Minnows held for periods much longer than a week although they may withstand the effects of starvation will become noticeably thin 3193 probably m l_e_a_§_s_ satisfactory _a_s_ bait than would minnows M 932 gig. 1113i}; salability because 23 their thinness §_n_<_i_ leak- ness would b_e_ lessened. Size as a Factor in the Mortality of Fathead Minnows In order to determine whether the size of a fathead minnow has any effect on its ability to survive in hold- ing tanks when either starved or fed, two methods or pro- cedures were followed. The procedures and results are described separately. Mortality among Large and Small Minnows When Separated According to Size In this method two tanks, Tanks 9 and 10, were stocked with minnows selected as to size. The minnows placed in Tank 9 ranged from.medium to large size and the minnows placed in Tank 10 ranged from medium to small size. The fish were sorted according to their ability to swim through a wire basket of one-fourth inch mesh. The wire basket was suspended from the side and at the top of Tank 10. Minnows from Pond 4 were placed in the basket. The fish that passed through the basket and into the aquarium were left in the tank. If, after several minutes, the minnows had not managed to pass through the basket they were put in Tank 9. Tank 9 held the larger minnows and Tank 10 the smaller ones. When fully stocked each tank contained 250 grams of minnows. Tank 9 contained 236 of the larger size min- nows. Tank 10 held 464 of the smaller fish, almost twice the number held in Tank 9. 69 70 Prior to the ninth week of the holding period there was only one week in which the losses occuring among the larger minnows were proportionately and numerically larger than the losses occurring among the smaller minnows. In the third week the loss of minnows was higher among the larger fish. During this week 109 of the larger fish died, this was almost half of the number placed in the aquarium. The large loss could not be accounted for on the basis of starvation alone. No other reason for the high loss was found, every condition here was apparently the same as the condition which existed in Tank 10. During the first two weeks of the holding period the loss among the larger fish was proportionately and numer— ically much lower than the loss sustained by the smaller fish. After the third week the loss among the smaller fathead minnows was still proportionately and numerically greater up to the beginning of the ninth week and still proportionately greater after that. The differences in the losses after the third week were not so pronounced as they were during the first two weeks. Figure 10 offers a comparison of the differences in mortality between the larger and smaller size minnows. .OH Mam» ca odes one; msodafia hoHHmEm can mafia; .m mama CH cams one? mBoGCaS hownma one .oo>hmpm was manssvs onwamdom aw mama msocdaa exam HHmam was omnda macaw hpadmphofi .oa ohsmfim 72 QOHmMm GZHQAom 2H ”MM”! 0 .r o n N H ,4 H 43 a ti _ A . Jn ‘III*'*II*‘ whom-HI_QHdlm II;I.II IL nIOZIHI Momdq nllllll Db HBHA‘HMQI 73 By the end of the first day of the second week of the holding period, 25 percent of the smaller fish had died and by the end of that same week 50 percent of these minnows had died. Seventy-five percent had died by the end of the fourth.week. At the end of the 12 weeks one minnow re- mained alive, less than 1 percent of the original number of minnows stocked in the aquarium. Among the larger min- nows 25 percent had died by the end of the first day of the third week, 50 percent had died by the end of the same week, and 75 percent had died by the end of the fourth week. After 12 weeks nine of the larger fish or 4 percent of the number stocked in the aquarium continued to live. It is to be noted that by the end of the seventh week the number of larger minnows still living exceeded the number of smaller minnows that continued to survive. The larger fathead minnows were able to withstand starvation more successfully than the smaller minnows. With the exception of the third week this appeared quite obvious. When fish are overcrowded in a tank and the oxygen content of the water is at a critical point Moore (1942) says that, "small fishes are less tolerant of low oxygen tensions than are larger fishes of the same species, at both summer and winter temperatures." It is believed that some factor other than malnutri- tion caused the large number of deaths among the large 74 minnows in the third week. In Tank 5 the smaller minnows seemed to be dying at a faster rate than the larger minnows held in the same aquarium. By the fourth week the physical condition of the minnows held in Tank 10 was very poor. Upon inspec- tion in the ninth.week the dead fish from Tank 10 were noticed to be in very poor condition. The larger mdnnows held in Tank 9 when examined in the eighth.week were in fair shape being thin but not wasted. Mortality of Large and Small Fathead Minnows Held in the Same Aquarium In this procedure all the minnows from Tanks 1 and 2 that died during or survived the l2 week holding period and all the minnows from Tank 7 that died in the 12 week period were placed and held in jars containing a 10 per- cent formalin solution until the spring of 1950. All the fish dying within a given week in a particular tank were placed in separate jars. The minnows that survived the 12 week period were killed, their brains being pithed, and placed in one of two Jars according to the tank from which they were taken. During the spring of 1950 a tabulation was made of the total length, to the nearest millimeter, of all min- nows held in Tanks 1, 2, and 7. Following the procedure it was found that the larger fathead minnows held better 75 under varied holding conditions than the smaller ones. The evidence for this fact was much more apparent here than in the method previously employed and described above. Although there was a slight fluctuation from week to week throughout the 12 week holding period in the average lengths of minnows held in Thnk 7, there was a rather steady rise in the weekly average lengths of minnows held in Tanks 1 and 2. In all three aquaria as Figures 11, l2, and 13 show, the smaller fish tended to die first, the larger fish hold- ing better. This held true regardless of the fact that some of the fathead minnows were taken from fertilized ponds and others from unfertilized ponds, that some of the minnows were more crowded than others, and that some of the fish were fed and others were not. Small fathead minnows are not able to withstand low oxygen tensions, and starvation as well as the large fathead minnows. .voaaoa mcavaon moo: NH one oo>H>93m fleas: msoddae mo muonw 03p nepmoaona m .anaoa wnavaon on» whaasc moan asap msocnaa mmonpmm ho Ammo: any npwcoa owsnepd .HH oasmam '7'7 NH HH OH DOHmMm uanqom IH mumm- o m b my a v q q d, H d \q 41 Id II IH NHGIHH flcdxflb< Hv av bv av .ooanoa weavaon moo; NH on» ca>a>95m dean; ascends ho anoam on» mopmoawda m .moflaom wcfioaon on» wcahsb node asap agendas omenpwu mo Axes: hnv npwqoa owmaopd .NH shaman 79 some: 0558 H a anyone“ and 3 3a as on e» a... 25». .ooanom wcfioaofl one mafiasm voac pane meonnas no Ammo: how npmdoa mmmaopd .na madman 81 Doumflm cmHQAom zH damn! _.m A. o e a a a . has ll NH mauzua flcdmflbd av 0v DISCUSSION It is necessary, in order to eliminate the large number of minnow losses in holding tanks, to understand in more than a vague and general way the nature of the minnow losses. It is not sufficient merely to know that condi- tions such as overcrowding, lack of cleanliness in the holding tanks, and lack of food contribute to the heavy minnow loss in holding tanks. It is also necessary to know when the minnows are or are not overcrowded, how and when dirty aquaria cause high minnow losses, and when the minnows should be fed and with what food. It was the purpose here to arrive at a better un- derstanding of the nature of minnow losses by investi- gating some of the factors responsible for this loss. Information from the work of other investigators concern- ing the life history of the fathead minnow and proper methods for holding minnows was included in order to com- plement the work reported on here. It was the endeavor to provide others, who employ this paper as a source of information, with a greater understanding of the nature of minnow losses and with the information necessary to reduce the excessive loss of minnows held in tanks prior to their sale. There are several avenues by which the findings of 82 83 these studies derive practical application. The findings are of use to bait dealers, are of value as a general con- servation measure, and are aids in pointing the way towards providing fisherman with better bait minnows. The findings should be of use to bait dealers because a greater insight into the nature of minnow loss is pro- vided. This insight furnishes a motive for avoiding unde- sirable holding conditions. The loss or waste of minnows results in a loss of time, energy, and money to the bait dealer. The implicit and explicit recommendations contained herein furnish means for reducing the excessive loss of minnows in holding tanks. The results of this work should be of value as a gen- eral conservation measure. Fish culturists, bait dealers, and sportsmen are concerned over the shortage of forage and bait minnows. This loss, as has been mentioned previously, has arisen from the wholesale removal of minnows from lakes, rivers, and streams by bait dealers in order to supply fishermen with bait minnows. The greater majority of the minnows so removed are lost or wasted. If this high loss and waste sustained in harvesting, transporting, and holding minnows is eliminated, the de- mands of bait dealers and fishermen could still be satis- fied by removing only a small portion of the minnows now 84 being removed. In removing only a small percentage of the minnows now removed, more minnows would be available as forage for the game fish, the result being better game fish. It is very probable that lakes, rivers, and streams now open to the taking of minnows would remain open and those now closed might be reopened. Fewer fish ponds would need to be built in order to satisfy the demand for bait minnows. The findings of this investigation point the way for providing fishermen with better bait minnows. Almost all the bait minnows being held in tanks are subject to very adverse conditions and as a consequence many of these fish are either on the point of death or are quite weak. Such fish make poor bait. These minnows would hold up so much better on the hook if their previous physical condition had been better. With the information and suggestions given here, it is possible to keep the bait minnows in good condition in the holding tanks. SUIVTMA RY l. The fathead minnows from the fertilized pond were better able to withstand the harmful effects resulting from having been handled than were the minnows from the unfer- tilized pond. 2. When the fathead minnows were held for long per- iods and starved, those frOm the fertilized pond held no better than those from the unfertilized pond. 3. In tanks approximately 30 inches long and 16 inches wide and containing 32 gallons of water which was aerated by compressed air, the maximum.number of fathead minnows that could be held without a large loss lay be- tween 19 and 35 minnows per gallon. 4. The loss of fathead minnows was lower in tanks where the fish excrement had been removed, and much lower in tanks where the dead minnows as well as the excrement had been removed. 5. At an average temperature of 680 F- and at a concentration of eight to nine minnows per gallon, the loss among minnows which had been held and starved for four weeks was only slightly greater than the loss among minnows which had been fed during the same four week period. 85 86 6. Large fathead minnows were better able to with- stand low oxygen tensions and starvation than the small minnows of the same species. 7. Crowded minnows do not feed as well as minnows which are not crowded. 8. The stomach of bait minnows tends to degerate when the minnows are held for long periods and fed on only dry foods. 9. Minnows held and starved for periods exceeding a week, although they may continue to live, will become no- ticeably thin. In this condition they would probably prove less satisfactory as bait than minnows which were fed. LITERATURE CITED DaViS, He So 1947. Care and diseases of trout. Research Report 12, U. 50 FiSh and Wildlife serVo, pp. 4‘77. Dobie, John R. 1948. Minnow propagation. Conservation Bull., No. 13, Minnesota Department of Conservation, pp. 4-20. Dobie, J. R., 0. L. Meehean, and G. N. Washburn 1948. Propagation of minnows and other bait species. Circular 12, U. S. Fish and Wildlife Serv., pp 0 71-105 0 Hubbs, Carl L. 1933. Some experiences and suggestions on forage fish culture. Trans. Am. Fish. 800., Vol. 63 (1933), pp. 53-63. Hubbs, C. Lo and K0 Fe Lagler 1947. Fishes of the Great lakes region. Cranbrook Institute of Science, pp. 68-69. Moore, Emmeline 1932. Certain minnows showing adaptibility to conditions in impounded waters. Trans. Am. Fish. 800., Vol. 62 (1932), pp. 290-291. Moore, Walter 1942. Field studies of the oxygen requirements of certain fresh water fishes. Ecology, Vol. 23, pp. 319-325. Radcliffe, Iewis 1931. Propagation of minnows. Trans. Am. Fish. 800., Vol. 61 (1931), pp. 131-138. 87 88 Schoenfeld, Clay 1949. Why not raise your own bait minnows? Fishing Annual, Sports Afield, (1949), pp. 16-19. Stoye, Frederick H. 1935. Tropical fishes for the home their care and propagation. Frederick H. Stoye, Publisher, Sayville, New Yerk, p. 13. Wynne-Edwards 1932. The breeding habits of the black-headed minnow (Pimephales romelas Raf.). Trans. Am. Fish. Soc., Vol. 62 (I932), pp. 382-383. ABSTRACT OF THESIS EXPERIMENTS IN THE HOLDING 0F BAIT MINNOWS BY BROTHER DONALD ALLEN, 0.3.0. In order to satisfy the fishermen's demand for bait minnows, bait dealers and fishermen themselves have rapidly depleted the supply of minnows in streams, rivers, and lakes where once these fish abounded. Most of the minnows that are taken from the streams, rivers, and lakes are lost or wasted. Because of the shortage of forage and bait minnows two methods for eliminating this shortage are receiving the attention of fish-culturists. The propagation of bait minnows in ponds is one of the means advocated for over- coming the shortage of minnows. The fathead minnow has many desirable features which recommend its propagation in ponds. Much of the loss and waste of minnows occurs in the tanks the fish are held in prior to their sale as bait. Im- properly constructed tanks, overcrowding, insufficient oxygen, lack of cleanliness, water that is not suitable for fish life, and too rapid changes in the temperature of the water are some of the causes of the large loss of minnows in holding tanks. Fungus and other pathological conditions are usually the result of unfavorable conditions prevailing in the holding tank. Brother Donald Allen, 0.8.0. 2 It was the purpose here to investigate some of the factors responsible for the large loss of minnows in holding tanks in order to develop means for eliminating the loss. Specifically, it was the aim of this work to determine: (1) whether minnows taken from fertilized ponds hold better than minnows taken from unfertilized ponds, (2) the maximum stocking capacity of an aerated tank, (3) the effect that cleaned and uncleaned tanks have on fish losses, (4) the mortality of minnows when they are fed and when they are starved, (5) the holding ability of large and small minnows. It was found that: (l) fathead minnows from an un- fertilized pond held as well as those from a fertilized pond, although the fathead minnows from the fertilized pond were better able to withstand the harmful effects resulting from their being handled than were the minnows from the un- fertilized pond, (2) in a 32 gallon tank 30 inches long and 16 inches wide and in which the water was aerated by compressed air, the maximum.number of minnows that could be held without large minnow losses lay between 19 and 35 minnows per gallon, (3) the loss of minnows in cleaned tanks was lower than the loss in uncleaned aquaria, (4) at an average temperature of 68°F. and when there was a light concentration of minnows in the holding tank, the minnows that were starved for four weeks suffered only a slightly higher loss than did the minnows which received food during the same period, (5) large fathead minnows were better able to withstand starvation than were small fathead minnows. Brother Donald Allen, C.S.C. There are several avenues by which the findings of these studies derive practical application. The findings are of use to bait dealers, are of value as a general conser- vation measure and are aids in pointing the way towards providing fishermen with better bait minnows. {g R. Q. {fig/M Room USE- 0‘“ . w 2 5,1994 ‘ qotflbto "mmm