RELATIONSHIPS OF A FISH POPULATION
TO THE RNV'ERTEBRATE FAUNA 1N TWC‘
SMALL PONDS

Thesis for fit. Degree a? M. S.
MICHKGMwl S?ATE COLLEGE
Hay-d Prim Wiikim

1952

0-169

Date

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This is to certify that the

thesis entitled

“Relationships of a. fish population
to the invertebrate fauna in
two small ponde.‘

presented by
Lloyd P. Wilkins

has been accepted towards fulfillment
of the requirements for

degree in Zoology

‘3

Major professor

March 12, 1952.

 

 

 

 

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stamped below.

 

RELATIONSHIPS OF A FISH POPULATION TO THE
INVERTEBRATE FAUNA IN TWO SMALL PONDS

BY

LLOYD PRICE WILKINS
“an...

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

4‘7 1"'/).5' u.
L”?

of

ACKNOWLEDGMENTS

This investigation was made possible through a coopera-
tive agreement between Michigan State College and the Michi-
gan Institute for Fisheries Research. Both institutions
provided equipment and financial assistance for the study.

My special appreciation is due Dr. Robert C. Ball, De-
partment of Fisheries and Wildlife, Michigan State College,
who directed the study and provided the source of encourage-
ment and generous cooperation necessary for its completion.

Sincere thanks are extended to Mr. Ralph Marks, Regional
Supervisor, and Mr. Henry Hatt, Hatchery Superintendent, of
the Michigan Department of Conservation's Fish Division for
their valuable assistance.

Mr. Thomas F. Waters assisted materially in all phases
of the field work during the latter part of the experiment.

I.
II.
III.

IV.

V.

VI.

VII.
VIII.
IX.
X.
XI.

TABLE OF CONTENTS

INTRODUCTION . . . . . . . . .
DESCRIPTION OF PONDS . . . . .
INVESTIGATIONAL TECHNIQUES AND
Stocking the Ponds . .
Bottom Sampling . . . .

Collection of Fish . . .
Laboratory Examination .

Bottom samples . . . . .
Stomach analysis . . . .

EQUIPMENT

0 O O O 0

DISCUSSION OF DREDGE SAMPLING DATA . . .

EFFECT OF FISH PREDATION . . .

Pond 4 O O O O O O O O O O
Pond 5 O O O O O O 0 O O O

FEEDING HABIT INVESTIGATION

Pumpkinseed Sunfish . . . .
Bluegills . . . . . . . . .

FORAGE RATIO DISCUSSION . . .
YIELD OF BOTTOM FAUNA AND FISH
STATISTICAL TREATMENT . . . .
SUMMARY . . . . . . . . . . .
LITERATURE CITED . . . . . . .

Page

10
ll

11
12

13
25

50
36

59

44
45

48
55
61
65
68

 

INTRODUCTION

The increasing demands made upon existing fish stocks
in bodies of water, due primarily to expanding fishing inten~
sity, have resulted in a more critical examination of fac-
tors controlling the magnitude of fish and fish food abun-
dance. With.more complete information concerning these lim-
iting influences, it may be possible to eXpand production at
one or more trophic food chain levels and subsequently in-
crease the yield of food organisms and fish at higher levels.

Maximum fish yield in an aquatic environment cannot ex-
ceed the ability of the habitat to produce the food neces-
sary for maintenance of normal metabolic activity and in-
crease in growth. Therefore, from.a fishery management
standpoint, the relationship of fish to their food supply is
perhaps the most important of the many interactions occur-
ring in the ecological complex of bodies of water. The in-
vestigation described here was designed to further our know-
ledge of this interrelation. The particular phase chosen
was that of a primary carnivore fish population to the ben-
thic fauna in small ponds.

A bottom fauna study was conducted to record the reac-
tion of invertebrate fauna to the introduction and removal of
a fish population closely dependent upon it. Two ponds,
similar in morphometric, physical, and biological character-

istics, were chosen for the experiment. One was stocked in

2
April, 1951 with fish and the other not stocked. Sampling of
the benthic fauna was begun immediately, and collections were
made at a uniform rate during May and June. During the first
week of July, the pond containing fish was drained, its fish
population removed, and was refilled immediately. The fish
were counted, weighed, and a poundage equal to that initially
released was transferred to the pond previously without fish.
Bottom sampling was continued at the same rate throughout
July and August until termination of the experiment the first
week of September. At this time the fish were removed to
allow determination of their increase in weight.

A feeding habit study was conducted concurrently with
the bottom fauna study to indicate not only the benthic
groups present in the environment but those actually impor-
tant in the food chain economy.

Another consideration involved the use of forage ratio
in tracing the variation in feeding habits of fish as the
composition of food items changed during the season.

A correlation between average standing crop of bottom
fauna and weight of fish produced from.it during the two
sampling and growth intervals is recorded. Certain of these
data were applicable to a study of food conversion by com-
paring the volume of benthic organisms ingested with the re-

sultant amount of fish growth.

DESCRIPTION OF PONDS

The two ponds used in this experiment are located at the
Wolf Lake State Fish Hatchery, 10 miles west of Kalamazoo in
Van Buren County, Michigan. They were selected for the study
because of their similarity in size, depth, basin conforma-
tion, bottom type, and common water supply. The ponds each
ghave a surface area of approximately one acre, a maximum
depth of 6.5 feet and an average depth of 3.0 feet. The
water supply is very high in carbonate hardness (160 p.p.m.)
and comes directly from a large spring which is the main
water supply for the hatchery. A nearly uniform water level
with a minimum of overflow was maintained at all times.
Black, organic muck covers the bottom of both bodies of water
except for a narrow fringe of sandy shoreline.

-A growth of 9232i developed over most of the bottom of
each pond (Figure 1) within three weeks after filling. The
only other higher vegetation to develop was a bed of Potamo-

geton pectinatus near the outlet of Pond 4. There was no

 

appreciable change in these plant beds as the season pro-
grassed.

Turbidity readings were made each week by means of a
Secchi disk. The disk was visible at the deepest point of
Pond 5 throughout the spring and summer. A phytoplankton
growth began to develop in Pond 4 the second week in May and

reached a climax on May 26 with a recorded Secchi reading of

Figure l. Pond 4 during the draining process.

 

 

 

' s! ileiav III .I .I'

6
56 inches. Five days of cold, rainy weather followed and 10
days later all traces of the bloom had disappeared. This was
the only plankton bloom observed during the experiment.

A plankton growth, induced by the application of ferti-
lizer, has been employed successfully to control undesirable
submerged aquatic plants (Smith and Swingle, 1942; Surber,
1945; Hogan, 1949; Swingle and Smith, 1950). The controlling
action is one of reduced light penetration causing photo-
synthesis to be retarded in the higher aquatic plants to a
point where they die.

Plankton turbidity in Pond 4 was of such short duration
it had no visible effect on the Chara and sago pondweed (P233;
mogeton pectinatus). The phytoplankton deve10pment may have

 

been due to the residual effect of fertilizer applied to this
pond as part of a fertilization project by Ball (1949) during
the summer of 1945. ‘

INVESTIGATIONAL TECHNIQUES AND EQUIPMENT

Stocking the Ponds

Bluegills (Lepomis macrochirus) and pumpkinseed sunfish

(Lepomis gibbosus) were selected as stock for the ponds be-

 

cause of their dependence for food upon invertebrate fauna.
A small number of redear sunfish (Lepomis microlophus) were
also released in an attempt to secure a more extensive usage
of mollusks and hard-bodied insects.

The initial release, made in Pond 4 on April 21, con-
sisted of 1,955 bluegills and 953 pumpkinseeds or a total of
124 pounds of sunfish per acre. These data plus the size

range and weight of the fish stocked are given in Table 1.

TABLE 1 ‘
SIZE RANGE, NUMBER, AND WEIGHT OF FISH IN ORIGINAL RELEASE

 

 

 

SiZeérange ““ ‘ Weight

Species (inches)* Number (pounds)
Bluegill 5.0- 4.8 1,415 52.5
409'- 708 515 4505
905.1000 7 600
Tota; - O O O O O O O O O O O O O O 0 1,935 O O O O 0 84.0
Pumpkinseed 2.0- 4.2 298 8.1
405' 6.0 655 3109
TOtal O O I O O O O 0 O O O O O O O O 955 O O 0 0 O 40.0

Total-~both

species 2,868 124.0

 

f—‘v

* Total length.

Fish of a wide size range were used to effect a more effic-
ient use of the available benthic fauna.

Following release of the fish, the variations in stand-
ing crop of benthic fauna due to fish predation, insect emer-
gences, and natural mortality were measured by bottom sampling.
Pond 5, containing no fish, was sampled at the same rate to
facilitate the quantitative comparison of bottom fauna abun-
dance in the two ponds.

Pond 4 was drained on July 3 and all fish were removed
for weighing and counting. The pond was allowed to refill
immediately in order to disturb its aquatic resources as
little as possible. The smaller size classes of fish, or
those approximating the size initially stocked in Pond 4,
were selected by screening and the exact poundage of each
species Originally released was transferred to Pond 5. This
release was made on July 9.

Bluegills, and to a lesser degree pumpkinseeds, are sub-
ject to heavy mortality due to handling. Most of the bane
dling losses which occurred the day of release and the day
following were recovered, weighed, and replaced by an equal
poundage.

Bottom sampling was continued throughout the remainder
of July and all of August to determine the effect of fish
predation on the abundant food supply of Pond 5 and to follow
the recovery of benthic fauna in Pond 4.

Also to be considered as pond stock are the thousands of

9
fry produced in Pond 4. Nesting activity was first noted on
May 9, but extensive spawning did not occur until the third
week of May. Most of the fry present when Pond 4 was drained
were less than one inch long and were probably incapable of
' seriously affecting the benthic groups dealt with in this
study. No young-of-the-year fish were transferred to Pond 5,
and the small number of fry produced there by late spawners
was inconsequential.

The average numerical loss of fish during the entire in-
vestigation was approximately 25 per cent of the population
of each of the three species concerned. This does not in-
clude the observed loss from handling. Complete data con-
cerning the release and removal of fish in the two ponds are
given in Table 2. The weight and number of fish removed at
the end of the two sampling intervals includes those taken

for stomach analysis.

Bottom.Sampling

The 660 random samples from the two ponds were collected
at the rate of 20 per pond per week during the period from
the last week in April through the last week in August. This
period corresponds with.most of the active growing season for
fish in Michigan.

All samples were collected using an Ekman dredge. The

Ekman dredge, by taking smaller samples and larger numbers

10
TABLE 2

NUMBER AND WEIGHT IN POUNDS OF FISH RELEASED IN AND
REMOVED FROM PONDS 4 AND 5

 

 

Bluegill Pumpkinseed Redear Totals

 

Released in Pond 4 No. 1,955 955 60* 2,928
4/21/51 Wt. 84.0 40.0 1.8 125.8
Removed from Pond44 No. 1,495 604 55 2,152
7/5/51 we. 140.0 51.5 5.7 195.2
Released in Pond 5 No. 845 590 52 1,487
7/9/51 Wt. 84.0 40.0 5.5 127.5
Removed from PondES No. 644 545 44 1,255
9/9/51 we. 105.2 52.2 5.8 171.2

 

* Released 5/14/51

of them, gave a better coverage of the pond bottoms than
would have been possible with a Petersen dredge. As each
dredge sample was raised, it was swung quickly into a pail

at water level. Later the pails, each containing one Ekman
sample, were taken to shore where their contents were washed
and concentrated in a 50-mesh screen and transferred to wide-

mouth fruit jars for return to the laboratory.

Collection of Fish

Fish for stomach analysis determinations were collected
with hook-and-line and by seining. Seventy-three pumpkin-

seeds, 121 bluegills, and 6 redear sunfish were collected.

 

11
These fish were weighed, sex determined, and measured immedi-
ately after capture and the stomachs, plus their contents,
placed in alcohol. It was found that more efficient removal
of the stomach contents could be facilitated by allowing the
stomachs to harden in alcohol for a short period before they
were opened. Immediate removal of the stomachs was necessary
to stop digestive action on the stomach contents (Ball, 1948).
An effort was made to procure fish of all sizes present in the
population to obtain a more complete understanding of their
use of available food. The effect of removal of these fish
on the benthic fauna density comparisons discussed later is
not considered serious since this loss was small compared with

the total population in the ponds.

Laboratory Examination
Bottom samples

Bottom samples were examined soon after collection, and
the organisms removed while still alive and active. Each
sample was given an identification number and preserved sep-
arately in 80 per cent alcohol until time allowed identifi-
cation and quantitative measurement of its contents.

Following division of the organisms into taxonomic
groups, they were counted and placed on absorbent paper to
remove excess liquid. Next, the volume of each group was de-

termined by the liquid displacement method using a centrifuge

12
tube graduated to 0.1 cubic centimeter. Total volumes were
recorded as each group was added to the tube, and the differ-
ence in the initial meniscus level and the last volumetric
reading was taken as the total volume for the sample.

For comparison of these data with those of certain other
investigators, 1 cc. of preserved volume can be considered
equal to 1 gram of live weight in accordance with calculations

made by Ball (1948).
Stomach analysis

A feeding habit investigation conducted as one phase of
this problem had as its primary purpose a qualitative compar—
ison of those bottom groups actually utilized by fish to a
significant degree with those known to be present by bottom
sampling. Consequently, only the taxonomic group and the num-
ber in each group were recorded. Many of the organisms were
identified, with the aid of a binocular microscope and refer-

ence collection, from fragmentary remains.

15

DISCUSSION OF DREDGE SAMPLING DATA

A tabulation of the sampling data for all organisms col-
lected by dredge in Ponds 4 and 5 is given in Tables 5 and 4.
In these summaries the invertebrate groups were recorded by
number and volume and by the percentage each comprised of the
total number and total volume collected each.month.

Trichoptera and planaria were significantly more abun-
dant in Pond 5 than in Pond 4. The fingernail clam (Pisidium),
while representing 12.2 per cent of the total volume of all
organisms collected in Pond 5, was not present in Pond 4.

Midges were numerically dominant in the fauna of Pond 4
from the last week in April through the last week in June and
represented 51.1 per cent of the total number of organisms
collected during that period. In July and August, the groups
present in greatest number were the mayflies Caenis sp. and

Centrgptilum spp. These two genera comprised 75.7 per cent

 

of all organisms by number. The seasonal average tabulation
for Pond 4 indicates the benthic groups in declining order of
numerical importance to be Caenis sp., midges, Oligochaeta,

Gastropoda, and Centroptilum spp. Volumetrically, the order

 

was Oligochaeta, Gastropoda, Hexagenia sp., and Caenis sp.

 

The seasonal average for the two mayfly genera (Caenis

and Centrgptilum) in Pond 5 was 55.6 per cent of the total

 

number and 8.6 per cent of the total volume of all organisms

collected. They were more numerous than other faunistic

 

 

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18
groupings throughout the season, excepting the month of July
when mollusks were dominant. In Pond 5, the invertebrate
groups in order of numerical significance were Caenis sp.,
Pelecypoda, Gastropoda, Chironomidae, and Centroptilum spp.
On a volumetric basis the order was Hexagenia sp., Gastropoda,
Oligochaeta, and Pelecypoda.

Groups included in the bottom sampling data but contri-
buting little to the seasonal totals in either pond were
Odonata, Tipulidae, Lepidoptera, and Hydracarina. The per-
centage composition of the total bottom fauna represented by
each.major invertebrate group is presented graphically in
Figures 2 and 5. This is done by number and volume for both
ponds.

The unnatural situation created by drainage of the ponds
and subsequent transfer of the fish from one pond to the
other was reflected in the numbers and volume of the bottom
organisms present. Consequently, comparisons concerning
abundance and importance of the bottom organisms in the two
ponds on a monthly or summer average basis must take these
factors into account. Also, comparisons among the different
groupings on a percentage of total volume basis are diffi-
cult, because the large volume groups (Gastropoda, Oligo-
chaeta, and Pelecypoda) tend to preclude the quantitative

values of other organisms more important as fish foods.

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23

EFFECT OF FISH PREDATION

The response of invertebrate fauna to the introduction
and removal of a fish population closely dependent upon it is
presented graphically in Figures 4, 5, 6, and 7. Figures 4
and 5 show the variations in total number and total volume per
square foot of all organisms collected by dredge sampling dur-
ing a 17 week period beginning April 24.

In Figure 4 certain systematic groups e.g. Hexagenia sp.,

 

oligochaetes, leeches, and large snails, because of their
greater volume, assume a dominant position over the groups
more important as fish foods. Because of the large percent—
age of the total volume represented by even a small number of
these individuals, the weekly volumetric fluctuations in
Figure 4 are probably due more to sampling dissimilarities
than predation by fish, insect emergence and mortality, and
other factors. However, these same groups helped to stabi-
lize the curves in the plot of total number per square foot
(Figure 5) since they were less subject to fish predation,
emergences, and mortality upon drainage of the ponds.

To present a more accurate representation of the rela-
tionship of a fish population to fluctuations in its food
supply, the graphs were replotted omitting the leeches, oli-

gochaetes, Hexagenia sp., and snails greater than 2 mm. in

 

diameter. The 2 mm. measurement represents the largest

diameter of any snail found in the fish stomachs analyzed.

 

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28
These corrected quantitative values are depicted in Figures
6 and 7. The curves of number and volume in the two figures
are very similar.

Hexagenia sp. and the oligochaetes together constituted

 

less than 1.0 per cent of the total number of organisms in
the stomachs analyzed, and no leeches were found. This ob-
servation confirms results reported by (Howell, 1942; Funk,
1942; Ball, 1948; Patriarche and Ball, 1949).

Seasonal fluctuations of invertebrate populations, and
the effects of removal of a fish population upon the bottom
organisms in a natural lake have already been studied by Ball
and Hayne (1952). Their data from Third Sister Lake in Michi-
gan showed a definite cycle of seasonal abundance and soar-
city of benthic organisms over a three year period with the
maximum occurring in early winter followed by a decline un-
til a minimum.is reached in early summer. Then in latter
July or early August the population began its rise toward a
new peak. A similar population cycle has been reported by
Deevey (1941) and Lyman (1945).

The study of Ball and Hayne (1952) shows further that the
normal seasonal population cycle, when released from preda-
tion by fish, did not reach so low a point as during the pre-
ceding year, and the upturn in volume of organisms per unit
area of bottom was much sharper than during the preceding
year. The preceding year referred to was the year 1940 when

a fish population, 85 per cent of which was estimated to be

29
directly dependant upon the invertebrate fauna, was present.

In this study no comparative data are available to give
the benthic density in the ponds for previous years, with and
without fish, as was done above. However, a situation anal-
ogous to the one described by Ball and Hayne is seen in the
‘sharp, upward p0pu1ation trend exhibited by the invertebrates
in Pond 4 when they, like those in Third Sister Lake, were
relieved of fish predation.

A rapid population decline in Pond 5, under the influ-
ence of actively foraging fish, gradually reduced the inver-
tebrate population from a high of 2.01 cc. and 270 organisms
per square foot the first week in July to a low of 0.54 cc.
and 81 organisms the last week of August when sampling was
terminated. Patriarche and Ball (1949), also working at the
Wolf Lake Hatchery with four similar ponds and the same faun-
istic groups, recorded the same downward tendencies at this
time and approximately the same reasons for their occurrence.
The population decline in Pond 5 is directly Opposed to the
annual upturn occurring at this time as reported by Ball and
Hayne, Deevey and Lyman. However, the decline is not an un-
natural one for the following reasons.

Patriarche and Ball attributed this deviation to (l)
the effects of predation by large numbers of young bluegills,
and (2) the emergence of numerically dominant midges. An
examination of the data for Pond 5 illustrates the same cause

and effect; the variation from the normal here being due to

50
predation by large numbers of young and adult sunfish and
emergence of numerically dominant mayflies.

A more specific discussion of the fluctuations in benthic
fauna abundance and reasons for their occurrence follows.
The numerical and volumetric values used have been corrected

for oligochaetes, Hexagenia sp., leeches, and snails greater

 

than 2 mm. in diameter.

Pond 4

Bottom.fauna were at a relative high of 1.02 cc. and 191
organisms per square foot (Figures 6 and 7) when bottom.sam-
pling began on April 21 but dropped to 0.21 cc. and 45 organ-
isms one week after the fish.were introduced. It is possible
that this decrease was greater than would have occurred norm-
ally since the fish had been held for 18 days without food
prior to their release. Moore (1941), working with green
sunfish (Lepomis cyanellus) that had been starved for a

 

period of five weeks, concluded that these fish after being
returned to their normal laboratory diet ingested consider-
ably more food and gained weight at almost twice the normal
rate of comparable unstarved individuals.

Midges were the most important insect group present,
both numerically and volumetrically, at the beginning of the
sampling period, and early emergences were partly respon-

sible for the early downward trend. Further evidence of en-

 

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55

suing emergences during this period is seen in the relatively
large numbers of midge pupae collected.

Following this decline the first week of sampling, the
standing crop of available organisms did not fall below a
fairly stable average of 65 organisms and 0.28 cc. per square
foot during May and June. Recorded fluctuations during this
period were probably due to insect emergences and sampling
inaccuracies. Midges remained the dominant group throughout
May and June and comprised 70.8 per cent by number and 60.1
per cent by volume of all organisms known to be important in
the diet of the fish present.

The rapid increase of insect fauna in Pond 4, when re-
lieved 0f fish.predation is most apparent in the two mayfly
genera (Caenis sp. and Oentroptilum spp.) as the eggs from

 

earlier oviposition and those instars previously too small to
be retained during screening of the samples developed. These
two genera alone rose from 11 organisms and 0.07 cc. per
square foot the first week in July to 558 organisms and 1.56
cc. the first week in August. This upward trend continued
until a large hatch of Caenis sp. the night of August 5 and a
second hatch on August 10 sharply reduced their numbers.
Further nocturnal emergences of Centroptilum spp. occurring
on August 15, 15, and 20 hastened the decline so apparent in
Figures 6 and 7. Small batches of mayflies were common
throughout August, but those taking place on the specific

dates just mentioned were sufficiently large to form.windrows

56

along the lee margins of the ponds.

Increases in the numbers of Zygoptera, Trichoptera, and
Coleoptera were also important in the population upturn of
July and early August. The total quantity of organisms
available as fish food increased from 45 organisms and 0.17
cc. to 416 organisms and 1.69 cc. per square foot during

this period.

Pond 5

Pond 5 was drained and allowed to remain nearly empty
for three days prior to its filling on April 26. Rep0pula-
tion occurred quickly and increasing numbers of Ephemerida,
Pelecypoda, and Trichoptera offset the loss by emergence of
midges and Zygoptera, resulting in a continuous increase from
129 organisms and 0.75 cc. per square foot the first week of
May to a maximum of 541 organisms and 2.46 cc. per square
foot the third week of June. Insect emergences were begin-
ning to have their effect, and a sharp decline, both in num-
bers and volume, occurred during the fourth week in June.
Plotted on semi-logarithmic paper a similar geometric rate of
decline is evident for both ponds at this time. It is indi-
cated that the influence causing this downward trend was
equally active in both situations thereby reducing the pos-
sibility that the smaller quantity of organisms collected was

a sampling disparity.

57

The effect of the fish population upon the benthic
organisms in Pond 5 is best seen in the abruptly declining
quantitative volume (Figures 4 and 6). Emergences of Zygop-
tera and Trichoptera, plus increased utilization of finger-
nail clams and snails by foraging pumpkinseeds and redear
sunfish, contributed most to the population reduction of
July and early August. More important in the decline were
the large numbers of small snails that appeared in the
samples the latter part of the summer. Although snails were
instrumental in upholding the numerical curve illustrated by
Figure 7, they represented a much.smaller percentage of the
total volume than they had previously. A marked reduction
in all groups except the Coleoptera occurred during the
month of August.

In spite of fish predation introduced the first week of
July there was no immediate decrease in the numbers of bottom
fauna. An increase in Coleoptera, Ephemerida, and Gastropoda
overcame any significant decline due to emergence of other
insect groups and the effect of fish utilization. Conse-
quently, the number of organisms was maintained at a nearly
constant level of 275 per square foot until the third week
of August. At this time, the large Caenis sp. and Centrop-
tilum spp. hatches previously mentioned for Pond 4 resulted
in a very rapid quantitative decline. These hatches occurred
during the same general period but never in both ponds on the

same night. Emergence periods usually alternated between

58

ponds and at two to five day intervals.

In summary, the volume of available benthic fauna in
Pond 5 without the limiting effect of fish predation in-
creased steadily from.0.75 cc. per square foot the first week
in May to a maximum of 2.46 cc. the third week of June. Then,
when exposed to predation by fish, the benthic population de-
clined from 2.01 cc. the first week of July to 0.54 co. the
last week in August.

It should be reiterated that numerical values used in
this section and the one previous represent only those organ-

isms important in the diet of the fish.

59

FEEDING HABIT INVESTIGATION

Many studies of the feeding habits of bluegills and
pumpkinseeds in natural waters have been made (Baker, 1916;
Pearse, 1918; Leonard, 1940; McCormick, 1940; Funk, 1942; Hof-
fett and Hunt, 1945; Ball, 1948; Ball and Tanner, 1951; Mor-
gan, 1951). The food analysis considered here differs from
most of those made previously since it concerns food consumed
in two, small, artificial ponds.

A total of 200 fish of the three species present in the
ponds were collected between May 6 and August 26. The 75
pumpkinseed stomachs were from fish ranging in length between
2.5 and 6.2 inches (total length) and having an average
length of 4.8 inches. The bluegills were larger, averaging
5.5 inches and were from 5.5 to 7.4 inches in length. Six
redear sunfish, having an average length of 4.9 inches, were
included in the study. Of the total number of stomachs ex-
amined, only 14 were empty. A summary of the data concerning
the fish used in the food study is given in Table 5.

Table 6 represents a tabulation of the stomach analysis
data for the pumpkinseed sunfish and bluegills and lists
each food grouping as the percentage it represents of the
total number of organisms and by the percentage of stomachs
containing each group. An examination of the redear sunfish
stomachs showed their feeding habits to be similar to those

of the pumpkinseed and bluegill excepting a decidedly greater

40
TABLE 5
DATA CONCERNING FISH REMOVED FOR STOMACH ANALYSIS

_. L

 

 

fi

Pumpkinseed Bluegill Redear

 

Number of fish 75 121 6
Length range (in.) 2.5-6.2 5.5-7.4 4.5—5.4
Average length (in.) 4.87 5.56 4.92
Weight range (gms.) 6-98 11-151 26-60
Average weight (gms.) 48.2 55.9 41.0
Total weight (pounds) 7.7 14.5 0.4

 

usage of snails and fingernail clams (Pisidium). These two
groups comprised 45.5 and 11.4 per cent, respectively, of the
stomach contents.

The stomach analysis data from fish of all sizes are
combined in one table since no significant differences could
be determined among the organisms utilized by the various
size classes. The only important difference observed among
the different size groups lay in the larger number of ostra-
cods consumed by the smaller fish.

Vegetation consumed as food refers to fragments of fila-
mentous algae, 92333) and in a few instances sago pondweed,

(Potamogeton pectinatus). Included under terrestrial insects

 

are small numbers of adult wasps, ants, and beetles. Organic

debris includes animal matter in such an advanced state of

Table 6. Food of adult pumpkinseed sunfish and
bluegills from Ponds 4 and 5. (Unless
otherwise indicated, all aquatic in- '
sects listed are immature stages.)

 

 

 

 

 

 

 

 

 

 

 

Pumpkinseed sunfish Bluegills
{umber of stomachs 73 121
Lumber empty stomachs 5 9
Total number organisms 2,517 10,177
Organisms per stomach 34-5 M -
Percent Percent
Percent stomachs Percent stomachs
Fish food organisms organisms containing organisms containing
by number organism by number organism
Aquatic insects
Midges
Chironomidae 27.48 60.27 24.87 26.00
Ceratopogonidae 7.35 46.58 3.10 23.76
Midge pupae 1.07 19.18 .17 6.53
Midge adults .32 9.59 .19 5. 3
Ephemerida
Caenis 11.36 34.25 3.86 20.6
Caenis adults .08 1.37 .37 5.3
Centroptilum 3.50 31.51 5.15 25.11
Centroptilum adults .04 1.37 .16 4.48
Hexagenia .16 4.11 .04 1.79
Odonata
Anisoptera .04 1.37 .08 .90
Zyg0ptera ..... ..... .20 5.83
Zygoptera adults .08 2.74 .25 .90
Hemiptera
Corixidae .12 4.11 .28 3.14
Corixidae adults ... ..... .01 .45
Coleoptera
Haliplidae 4.37 45.21 .84 13.00
Haliplidae adults .12 2.74 .03 .90
Trichoptera .52 4.11 .10 3.59
Lepidoptera .36 1.37 . ... .....
Crustacea
Cladocera 23.08 42.47 55.26 27.80
Ostracoda .32 8.22 .37 5.38
Decapoda .04 1.3g .06 2.24
Hydracarina .20 5. .52 8.97
Gastropoda 17.48 54.79 2.80 16.59
Pelecypoda .36 4.11 .61 2.24
Oligochaeta .08 2.74 .01 .45
Hematoda 1.43 24.56 .54 11.21
Terrestrial insects .04 1.37 .04 1.79
Vegetation ..... 30.14 ..... g 18. 8
Organic debris ..... 34.25 ..... 22- 2
Inorganic debris ..... 15.07 . ... 1.79

 

 

 

 

 

45
decomposition or of such a fragmentary nature as to make it
unidentifiable. Inorganic debris refers to grains of sand
which were probably picked up accidentally.

The large aquatic earthworms, smaller tubificids, and

burrowing mayflies, Hexagenia sp., were relatively unimpor-

 

tant as fish foods, because their burrowing habit made them
unavailable to the fish. These groups combined represented
only 0.24 per cent of the pumpkinseed diet and 0.05 per cent
of the bluegill diet.

The use of Odonata and Trichoptera as fish food was
slight but in proportion to presence of the two groups in the
bottom samples.

Representatives of the order Hemiptera were common along
the margins of both ponds during the latter part of the sums
mer. Members of the families Gerridae, Notonectidae, and Cor-
ixidae were all numerous, but only nymphal and adult Corixids
were present in the stomachs. This preference has been noted
by Leonard and Leonard (1949) in their work with trout and is
probably related to the piercing bite and characteristic odor
some of the bugs possess. The Corixidae have neither of
these offensive qualities and consequently would seem to be a
more desirable food item.

The feeding habits of the pumpkinseeds and bluegills in
the ponds were generally similar except for a greater utili-
zation of snails and beetle larvae by the pumpkinseeds.

A more detailed account of the dietary components in the

44

pumpkinseed and bluegill stomachs follows.

Pumpkinseed Sunfish

Midges constituted the principal item in the pumpkin-
seed sunfish diet and composed 56.2 per cent of the total
number of organisms in the stomachs. The Chironomidae were
present in 60.2 per cent and the Ceratopogonidae in 46.5 per
cent of the stomachs examined.

The planktonic crustacean, Daphnia, was second in numer-
ical importance, representing 25.0 per cent of the total num-
ber of organisms and was found in 42.4 per cent of the stomachs
collected. The small creeping mayfly, Caenis sp., was espec-
ially susceptible to capture by the fish during its transfor-
mation periods and ranked fourth by numbers while appearing
in approximately one-third of the stomachs.

Snails made up 17.4 per cent and appeared in.more than
one-half of the stomachs, which would indicate them to be a

preferred food. Centroptilum spp. and the Haliplidae were

 

nearly equal in importance, comprising 5.5 and 4.5 per cent
of the total number. Even though their rate of incidence

was low, they were present in 51.5 and 45.2 per cent of the
fish. The selection of snails and hard-bodied insects e.g.

Haliplus and Peltodytes spp. is characteristic of the pump-

 

kinseed as evinced by other investigations (Baker, 1916;
Funk, 1942; Ball, 1948; Ball and Tanner, 1951). This utili-
zation did not extend to the fingernail clam (Pisidium).

45

The dietary habit of the pumpkinseeds varied from the
results recorded by McCormick (1940), Ball (1948), Ball and
Tanner (1951), due to the presence of vegetation, chiefly
93322) in 50.1 per cent of the stomachs as compared to only
18.5 per cent for the bluegills. 92323 composed more than
half of the contents of those stomachs containing it, pre-
cluding the possibility that it may have been taken acciden-
tally. Furthermore, there appeared to be no direct relation-
ship between incidence of the 92222 and quantity of food
available as the season progressed. It is probable that the
food supply never did reach a critical low necessitating the
substitution of plant material for aquatic insects in the
diet of the fish.

Bluegills

The small size and large number of Cladocera present in
those stomachs containing them tend to magnify their numer-
ical importance. Bluegills taking cladocerans fed on them
almost to the exclusion of other foods. Although no quanti-
tative determinations were made of the zooplankton in the
ponds, few cladocerans were noted by visual observations.
However, they formed the largest percentage of organisms by
number (55.2) and also ranked first in frequency of occur-
rence among the stomachs analyzed.

Chironomidae were second in importance, constituting a

46
numerical percentage of 24.8 and present in 26.0 per cent of
the stomachs. Computed on a numerical basis, midge larvae
were the dominant organisms in the stomachs examined during
the early part of the sampling period, and zooplankters were
of principal importance the latter portion of the experiment.
Further, during the spring and early summer, midges were as
numerous in some stomachs as zooplankters were in others
later on. For this reason, no attempt was made to correct
for the dominating influence of these two systematic cate-
gories upon the remaining food groupings. This dominating
tendency should be remembered when interpreting the percen-
tage composition by number tabulation since percentages
assigned to other food groupings are subsequently lower.
Relative values or the order of importance among the various
dietary groups remain unchanged.

Other groups of importance in descending order of fre-

quency were the mayfly (Centroptilum spp.), the creeping

 

mayfly (Caenis sp.), Ceratopogonidae and Gastropoda. These
groups were taken by fish in nearly equal numbers.
Hydracarina and Ostracoda were eaten consistently during
the sampling period but in comparatively small quantities.
Only one stomach (bluegill) contained sunfish fry and
this item was not entered in the food organism tabulation.
In nearly all of the stomachs containing ghggg, it com-
posed more than one—third of the contents. Filamentous

algae was present as infrequent fragments, occurred in only

47
5 per cent of the stomachs, and may have been taken inciden—
tally while feeding.

Oligochaetes and Hexagenia sp. were also of negligible

 

importance in the bluegill diet, being responsible for only

0.05 per cent of the total number of organisms consumed.

48

FORAGE RATIO DISCUSSION

The relationship of the organisms found in the stomachs
of a fish population to the fauna found in the fishes' en-
vironment is a complicated one. The most widely used ap-
proach to an estimate of the existing quantity of food organ-
isms represented by an aquatic fauna is the "measure of food
preference" by Hess and Rainwater (1959). This was referred
to as "forage ratio" by Hess and Swartz (1940) and was de-
fined by them as the ratio of the percentage which a given
kind of organism makes up of the total stomach contents to
the percentage which this same organism makes up of the total
population of organisms in the fish's environment. They ex-
plained further that where a group of organisms has a forage
ratio significantly different from one, it should be the
result of either a difference in availability or a difference
in preference.

Leonard (1942) questioned the use of "preference" to
describe the degree of utilization of organisms by fish. He
suggested that forage ratio be used as a method for measuring
availability instead of preference. |

Allen (1942) renamed forage ratio "availability factor"
but recognized the possibility of selection or preference on
the part of the fish.

Regardless of the name given the ratio of the percentage

occurrence of items in the stomach contents to their percen-

49
tage occurrence in the bottom samples, it has some useful
applications.

Surber (1941) used the methods of Ross and Swartz for
forage ratio and effective food grade determinations in his
work with.smallmouth bass streams.

Patriarche and Ball (1949) compared availability factors
(using numerical data) for organisms in fertilized and un-
fertilized ponds and their use by young-of-the-year bluegills.

Ball and Tanner (1951) utilized forage ratio to point
out the intermediate nature of food selection by pumpkinseed
x bluegill hybrids as compared to food used by their parent
species.

Ball (1948) compared variation in forage ratio values of
five benthic groups over a 5 year period in a natural lake.

It is evident from his investigation that values assigned to
food groupings will vary from year to year in the same body
of water. His data also show a wide disparity in forage
ratios computed from volumetric determinations and those
calculated from numerical data. However, it remains an open
question as to which gives the most accurate values for re-
lating food consumed to forage available.

Leonard (1949) favored the use of numbers and frequency
of occurrence in the stomachs rather than volume for recording
food data. He included volume measurements to facilitate com-
parison with other published reports. Allen (1942) stated

that availability factors determined from volumetric, gravi-

50
metric, or numerical observations can be used interchangeably
with reasonable accurracy. Hess and Swartz (1940) used num-
bers for their computations of forage ratio and food grade
values of bottom fauna groups as related to their occurrence
in the diet of black-nose dace. They state that the use of
weight or volume might be preferable for these determinations.

Uneven distribution of the bottom fauna and other forage
organisms has been cited as a principal source of error in
comparing densities of different faunas present in streams
(Surber, 1941; Allen, 1942). Fortunately, the pond bottoms
sampled in this investigation provided a nearly uniform en-
vironment for benthic fauna, and wide differences in number
and volume among the bottom samples did not occur.

The occurrence of seasonal variations in population den-
sity among the important food organisms is a well recognized
fact. To minimize the error these fluctuations might intro-
duoe in availability factor determinations, Allen suggested
that faunistic collections be taken throughout the year in-
stead of at one season. Since the primary use of forage
ratio concerns the nutritional benefit a fish receives from
organisms in its environment, it would seem that these de-
terminations would be more useful if made during the active
feeding and growing season of the fish. The reduced rate of
digestion and assimilation during the winter period is well
established (Markus, 1952; Leonard, 1942), and forage ratios

determined during this period of reduced metabolic activity

51
would neither be useful nor correct.

Forage ratio is used in this study to compare the utili-
zation of various food items as they vary in quantity through-
out a summer. For this comparison the important fish food
groups, as determined from the stomach analysis data, were re-
calculated on the basis of their representing 100 per cent of
the stomach contents. The corresponding groups among the bot-
tom fauna were revised in like manner.

Tables 7 and 8 present this variation for the pumpkinseed
sunfish and bluegill from May through August and give the
average forage ratio values and their components for the 4
month period. It should be remembered that the sampling data
listed under May and June were collected while the fish popu-
1ation was present in Pond 4. The data under July and August
were taken after transfer of the fish to Pond 5.

Midges consistently represented a greater percentage of
the total stomach contents than their relative abundance among
the bottom samples would indicate. This increased rate of
utilization, probably a food preference, is apparent for both
species of fish throughout the sampling period.

The large number of Ephemerida present in Pond 5 during
July and August is reflected in their increased usage by both
species of fish. A

The Odonata formed an important dietary item for the

bluegills in comparison to their small numbers available.

52
A reduced utilization of coleoptera larvae is indicated
for the pumpkinseed sunfish after transfer to Pond 5 where

more available and/or desirable foods were present.

COMPARISON
WITH

TABLE 7

OF FOOD UTILIZED BY PUMPKINSEED SUNFISH
THE VARIATION IN FOODS AVAILABLE

 

 

 

 

Pond 4 Pond 5‘
Food groups May June July August Average
Midges A 78.24 57.50 5.48 1.51 55.18
B 96.02 52.59 26.95 5.05 44.59
C 1.22 .91 7.74 2.00 1.26
Ephemerida A 10.78 6.49 55.50 75.78 51.58
B .18 2.87 28.52 60.55 22.92
C .01 .44 .80 .81 .72
Gastropoda A 7.88 27.51 42.69 5.25 20.85
B 5.44 27.04 56.72 55.55 25.15
C .45 .98 .86 6.54 1.20
Coleoptera A .28 6.56 10.44 15.95 7.80
B .56 17.70 5.08 2.75 .64
C 1.28 2.69 .48 .19 .08
Trichoptera A 1.41 1.61 7.12 4.98 5.75
B 0.... .0... 2.54 .28 1.31
C .0... .0... .52 .05 .34
Odonata A 1.41 .20 .62 .45 .67
B .0... 0.00. 0.0.. .00.. 0....
C 00.0. .0... .0... 0.... .0...
Hemiptera A .15 .55 .08 .18
B .000. .00.. .59 .28 .43
C .0... .0... 1.68 5.50 2.38
A -- Per cent in bottom samples by number.
B -- Per cent in stomach samples by number.

0 -- Forage ratio.

TABLE 8

COMPARISON OF FOOD UTILIZED BY BLUEGILLS WITH
THE VARIATION IN FOODS AVAILABLE

 

 

 

 

Pond 4 Pond 5
Food groups May June July August Average
Midges A 78.24 57.50 5.48 1.51 55.18
B 98.47 89.75 18.11 7.10 55.55
C 1.25 1.56 5.20 4.70 1.51
Bphemerida A 10.78 6.49 55.50 75.78 51.58
' B .45 6.12 58.86 81.79 51.80
C .04 .94 1.10 1.10 1.00
Gastropoda A 7.88 27.51 42.69 5.25 20.85
B .80 1.79 27.58 7.09 9.51
C .10 .06 .64 1.55 .44
ColeOptera A .28 6.56 10.44 15.95 7.80
B . 1.22 8.22 2.14 5.86
C ..... .18 .78 .15 .49
Trichoptera A 1.41 1.61 7.12 4.98 5.75
B .11 .19 .14 1.08 .58
C .07 .ll .01 .21 .10
Odonata A 1.41 .20 .62 .45 .67
B .17 .85 2.51 .80 1.08
C .12 4.25 4.04 1.77 1.61
Hemiptera A o o o o o 013 055 008 018
B .0... .09 4060 .0... 2.34
C .0... .69 13.14 0.... 13.00
A -- Per cent in bottom samples by number.
B -- Per cent in stomach samples by number.

0 -- Forage ratio.

55

YIELD OF BOTTOM FAUNA AND FISH

An outline for a study of fish and fish food production
is presented by Ricker (1946) using a critical analysis of
existing literature to formulate proposed principles and
methods. Such an understanding of the complexities of the
production at various trophic levels would be helpful in the
intelligent manipulation of factors leading to increases in
yield at any one and subsequently in all succeeding trophic
levels. The many interrelated phases of the productivity in-
vestigation pr0posed by Ricker include a consideration of the
annual net production of food organisms, the fraction of
existing organisms actually consumed by fish, factors affect-
ing amount and rate of feeding by fishes, and the conversion
of food to fish flesh.

Because of the many complexities involved in production
studies, wide use has been made of the more easily determined
relationship between summer standing crop of benthos and the
weight of fish produced from it (Meehean, 1956; Howell, 1941;
Smith, 1947; Ball, 1948). Meehean and Howell compared the
effect of fertilizer on production in southern ponds. The
work of Smith and of Ball was conducted on natural lakes in
Nova Scotia and Michigan, respectively. The standing crop
figure is a useful one since it represents the excess of food
material produced over the material destroyed by the many fac-
tors acting to limit its magnitude. Standing crop is, there-

56
fore, a measure of end result or food present at a given time
while production gives the amount entering the aquatic area
per unit time (Clarke, 1946).

No direct comparison exists between southern ponds,
natural lakes, and the shallow Wolf Lake Hatchery ponds be-
cause of the diverse nature of these waters. Nevertheless,
it is interesting to note that the total standing crop of
benthic organisms in pounds per acre was considerably higher
in the two Wolf lake ponds than in the southern bodies of
water and northern lakes just mentioned. However, when
those systematic groups not utilized by the fish are elim-
inated from the total standing cr0p average, the resulting
quantity is less than that reported by the other workers
except Smith (1947).

Data concerning fish growth in Ponds 4 and 5 are limited
to short periods of time because of the manner in which the
experiment was conducted. The following conclusions re-
lating standing crop of food organisms to yield of fish are
made with the objective of contributing to the meager store
of information dealing with this subject.

The 124 pounds of bluegills and pumpkinseed sunfish re-
leased in Pond 4 on April 21 increased in weight to 191.5
pounds by July 5 when they were removed for weighing and
transfer to Pond 5. Net increase for the 10 week period
was 67.5 pounds or a net gain of 6.4 pounds per week. The

average standing crop of important fish food organisms

57
during the period was 0.56 cc. per square foot or approxi-
mately 54.5 pounds per acre.

On July 9 the same weight of each species originally re-
leased in Pond 4 (124 pounds) was transferred to Pond 5. In
addition, 5.5 pounds of redear sunfish were transferred. A
not gain of 41.4 pounds, or 5.2 pounds per week, occurred by
September 9 when 171.2 pounds of fish.were removed and
weighed. These fish had available a benthic fauna averaging
1.15 cc. per square foot or approximately 110.4 pounds per
acre for the 8 week periods.

The standing crop average of 0.28 cc. per square foot
for the May-June period represents a fairly stable average
food level (Figure 6) and was supporting 195.2 pounds of sun-
fish per acre the first week in July. This poundage includes
5.7 pounds of redear sunfish.

Using data available for the May-June interval, it is
possible to compute the ratio of food conversion in Pond 4.
Only during this period can direct comparisons be made be-
tween the two ponds beginning with the same approximate food
level.

To calculate this conversion ratio, the following assump-
tions must be made. .

(1) The two ponds were alike in production of fish food
organisms.

'(2) The difference between the average bottom fauna

abundance values in the two bodies of water was directly

 

58
attributable to fish utilization.

(5) The rate of food production or "turnover" was not
appreciably different in the two ponds.

The similarity of the two ponds as to morphometry, water
supply, bottom type, and benthic populations has been dis-
cussed under pond description.

The numbers of organisms entering the size range usable
by the fish in Pond 4 were also responsible for the increased
abundance of food organisms in Pond 5. Consequently, this
difference in food levels should equal approximately the
quantity of benthic fauna necessary to produce the recorded
increase in fish poundage.

Although there were many more organisms in Pond 5, most
were insect larvae or nymphs and not of a stage of maturity
to add their progeny to the available food supply during the
short 2 month period.

If the foregoing assumptions are tenable then volume of
the standing crop of food organisms for Pond 5 during May and
June (1.66 cc. per square foot) minus the average volume in
Pond 4 (0.28 cc. per square foot) equals 1.58 cc. per square
foot or the quantity of food utilized by the fish. This
volume in cubic centimeters can be converted to grams within

reasonable limits of error by using the conversion factor

 

1 cc. preserved volume a 1 gram live weight (Ball, 1948).
Consequently, 1.58 grams per square foot x 45,560 square

feet in one acre equals 152.5 pounds per acre of those bottom

59
fauna known to be important in the fish.diet. Further, the
152.5 pounds of bottom fauna per acre divided by the net
poundage gained by the fish (69.4 pounds) represents a food
conversion ratio of 1.9. Stated differently, it took 1.9
pounds of bottom organisms to produce one pound of fish

flesh.

TABLE 9
DATA FOR CALCULATION OF CONVERSION RATIO

 

 

Food level in Pond 5 . . . . . 159.4 pounds/acre
Food level in Pond 4 . . . . . 26.9 "
Difference in levels . . . . . 152.5 "
Weight of fish removed . . . . 195.2 '3
Weight of fish released . . . 125.8 "

Increase in weight . . . . . . 69.4 "

152.5 _ l. d-
Conversion ratio . . . m 9 poun 5

 

The conversion ratio obtained by this method is prob-
ably low because the importance of planktonic forms in the
stomachs, while low volumetrically, was not accounted for as
available food. Also, the added value of plant material in
the diet is not known. 'A factor acting to lower the benthic
abundance level in Pond 5 might be the effect of midge emer-

gences. These hatches would be more important in the Pond 5

60
food level because of the larger number of individuals present
there.

Moore (1941) fed beef and beef liver to a specimen of

green sunfish (Lepomis cyanellus) for a 6 week period and ob-

 

tained a food conversion ratio of 1.9. Ratios for other

green sunfish, bluegills (Lepomis macrochirus), yellow perch

 

(Perca flavescens), and a pumpkinseed sunfish (Lepomis gib-

 

 

92223) ranged from 2.5 to 5.7. The work of Titcomb, Cobb,
Crowell, and McCay (1929) shows that brook trout require from
1.1 to 5.8 units of dry food to produce one unit increase in
body weight.

Although the estimate of food ingested to effect the ob-
served increase in weight is probably conservative, the tech-
nique is a suggested method for determining this ratio under
natural conditions rather than in the highly artificial situ-
ation created by confinement of the fish in aquaria or

hatchery ponds.

STATISTICAL TREATMENT 61

The standard error of the weekly average volume of organ-
isms per square foot was calculated for each of the ponds
(Table 10). Two standard errors were then plotted on either
side of the weekly mean and connected by narrow lines as 11-
lustrated in Figure 8. Since the weekly volumes per square
foot (connected by heavy lines) each represent an average of
20 samples representative of the benthic population in the
ponds, the probability that the true population mean falls

within the limits indicated is 95.45 per cent.

TABLE 10

TABLE SHOWING AVERAGE VOLUME OF BENTHIC ORGANISMS
PER SQUARE FOOT AND STANDARD ERROR

 

 

 

Pond 4 Pond 5
Week Mean vol. Stan. error Mean v01. Stan. error

April 4 1.02 .1940

May 1 .21 .0540 .75 .1576
2 .20 .0284 .91 .1020
5 .27 .0484 1.50 .2596
4 .28 .1052 1.65 .1252

June 1 .57 .0820 1.89 .2676
2 .50 .0528 2.57 .2604
5 .58 .0616 2.46 .5224
4 .25 .0580 1.85 .1884

July 1 .17 .0268 2.01 .2740
2 .65 .0764 1.92 .2196
5 1.06 .1412 1.25 .1540
4 1.47 .1704 1.27 .1920

August 1 1.70 .1912 1.02_ .1456
2 1.42 .1556 .67 .0940
5 1.25 .1244 .72 .0808
4 .79 .0704 .55 .0296

 

62

Figure 8 is essentially a modification of the graphical
method of Dice and Leraas (1956) and may be used for com-
paring mean weekly values within and between the two ponds.
Where the two standard error limits do not overlap, the dif-
ference between the mean values are significant at approxi-
mately the one per cent level. Overlapping limits imply that
there is no significant difference between average weekly
volumes of organisms per square foot. A further analysis of

these differences is possible through use of a standard "t"
test. '

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65

SUMMARY

The standing crop of benthos in two paired ponds was
compared at weekly intervals following the introduction
of a fish population into one of them. A benthic abun-
dance level approaching a balance between food organisms
consumed and those entering a size range usable by the
fish was reached less than one week after release of the
fish. The number and volume of bottom fauna increased

steadily in the pond without fish during this period.

Upon transfer of the fish to the other of the matched
ponds in midsummer, two directly opposed trends occurred.
The benthic population relieved of fish predation in-
creased in volume per square foot 7.5 times within 5
weeks until checked by heavy mayfly emergences. Mean-
while, the pond subjected to predation declined steadily
in benthic abundance until it reached a point approxi-
mating the food level previously recorded for the other

pond when it held fish.

The benthic groups of consequence in the bluegill and
pumpkinseed sunfish diet comprised only 24.1 and 57.0 per
cent by volume of the total invertebrate fauna collected
by dredge sampling. By number, the percentages were 82.7
and 86.1, respectively, of the total. Obviously, any
study relating fish yield to their food supply must con-

4.

6.

7.

66
sider these variations in organisms present, available,

and consumed.

Analysis of bluegill and pumpkinseed stomachs showed
their dietary habits to be similar excepting a greater
usage of snails and hard-bodied insects by the pumpkin-
seeds. It is indicated that midges were a preferred
food of both species as evinced by the proportionately
greater incidence of this item in the diet than in the
available food supply.‘ Other food groups were generally

taken in relation to the quantity available.

The percentage composition of various groupings making up
the total bottom fauna p0pu1ation changed considerably as
the season progressed. This variation, due primarily to
insect emergences and development, was also evident in

the composition of organisms represented in the bluegill

and pumpkinseed sunfish diets.

A correlation between average standing crop of fish food
organisms and the weight of fish produced from it can be
made for the first half of this investigation. Food
consumption balanced supply at the average level of 54.5
pounds of fish food organisms per acre during this 10
week period and gain by the fish equaled 54 per cent of
their original weight (69.4 pounds).

The efficiency of food conversion was also calculated for

67
the first sampling period, using the difference in aver-
age food levels in the two ponds as the amount of food
ingested to produce the increased weight of fish ob-

tained. The conversion ratio obtained was 1.9.

68

LITERATURE CITED

Allen, K. Radway
1942 Comparison of bottom faunas as sources of avail-

able fish food. Trans. Am. Fish. Soc., 1941,
71: 275-285. ’

Baker, Frank C.
1916 The relation of mollusks to fish in Oneida Lake.
Tech. Publ. 4, N. Y. State Coll. Forestry,
16: 1-566

Ball, Robert C.
1948 Relationship between available fish food, feeding

habits of fish and total fish production in a
Michigan lake. Tech. Bull. 206, Michigan State
College Agr. Exp. Sta., March, 1948.

1949 Experimental use of fertilizer in the production
of fish-food organisms and fish. Tech. Bull. 210,
Michigan State College Agr. Exp. Sta., March, 1949.

----------- and Howard A. Tanner
1951 The biological effects of fertilizer on a warm-
water lake. Tech. Bull. 225, Michigan State
College Agr. Exp. Sta., April, 1951.

----------- and Don W. Hayne
1952 Effects of the removal of the fish populations on
the fish-food organisms of a lake. Ecology (in
press).

Clarke, George L.
1946 Dynamics of production in a marine area. Ecol.
Monog. 16: 521-555.

Deevey, Edward S.

1941 Limnological studies in Connecticut. VI. The
quantity and composition of the bottom fauna of
thirty-six Connecticut and New York lakes.f Ecol.
Monog. 11(4): 415-455.

Dice, Lee R. and Harold J. Leraas
1956 A graphic method for comparing several sets of
measurements. Contrib. Lab. Vert. Gen. Univ.
B€iCho, 3: 1'3.

69

Funk, John
1942 The food of bluegills, perch, and pumpkinseeds
from Wintergreen Lake, Michigan, for 1955-1958.
Unpublished Report No. 790, Michigan Inst. for
Fish. Res., June, 1942.

Ross, A. D. and J. H. Rainwater
1959 A method for measuring the food preference of
trout. Copeia No. 5, Sept. 9, 1959: 154-157.

----------- and Albert Swartz
1940 The forage ratio and its use in determining the
food grade of streams. Trans. Fifth N. A. Wild-

life Conf. 162-164.

Hogan, Joe -
1949 The control of aquatic plants with fertilizers in
rearing ponds at the Lonoke Hatchery, Arkansas.
Trans. Am. Fish. Soc., 1946, 76: 185-189.

Howell, Henry H.
1942 Bottom organisms in fertilized and unfertilized
ponds in Alabama. Trans. Am. Fish. Soc., 1941,
71: 165-179.

Leonard, Justin W.

1940 Further observations on the feeding habits of the
Montana grayling (Thymallus montanus) and the
bluegill (Lepomis macrochiruST In Ford Lake,
Michigan. ITrans. Am. FifihifiSoc., 1959, 69:

244: “256 o

 

 

1942 Some observations on the winter feeding habits of
brook trout fingerlings in relation to natural

food organisms present. Trans. Am. Fish. Soc.,
1941, 71: 220-227.

----------- and F. A. Leonard
1949 An analysis of the feeding habits of rainbow trout
and lake trout in Birch Lake, Cass County, Michi-
gan. Trans. Am. Fish. Soc., 1946, 76: 501-514.

Lyman, F. Earle
1945 A pre-impoundment bottom fauna study of Watts Bar
Reservoir area (Tennessee). Trans. Am. Fish. Soc.,
1942, 72: 52-62.

Markus, Henry C.
1952 The extent to which temperature changes influence

food consumption in largemouth bass (Huro floridana).

Trans. Am. Fish. Soc., 1952, 62: 202-2IUT

 

7O

McCormick, E. M.
1940 The study of some Reelfoot Lake fishes. Jour.
Tenn. Acado 8010, 10: 65-750

Meehean, 0. Lloyd

1956 Some factors controlling largemouth bass produc-
tion. U. S. Bur. Fish., Prog. Fish. Cult.,
16: 1'60

Moffett, J. W. and Burton P. Hunt
1945 Winter feeding habits of bluegills and perch in
Cedar Lake, Washtenaw County, Michigan. Trans.
Am. Fish. Soc., 1945, 75: 251-242.

ioore, Walter G.

1941 Studies on the feeding habits of fishes. Ecology

Morgan, George D.
1951 The life history of the bluegill sunfish, Lepomis
macrochirus, of Buckeye Lake (Ohio). Denison
Univ. Bu11., Jour. Scientific Labs., 42(4): 21-59.

Patriarche, Mercer H. and Robert C. Ball
1949 An analysis of the bottom fauna production in for-
tilized and unfertilized ponds and its utilization
by young-of—the-year fish. Tech. Bull. 207,
Michigan State College Agr. Exp. Sta., May, 1949.

Pearse, A. S.

1918 The food of the shore fishes of certain Wisconsin
lakes. U. S. Bur. Fish. Bull., 55: 247-292.

Ricker, William E.
1946 Production and utilization of fish populations. 1
E001. Monog. 16: 575-591.

Smith, E. V. and H. S. Swingle
1942 The use of fertilizer for controlling several sub-
merged aquatic plants in ponds. Trans. Am. Fish.
Soc., 1941, 71: 94-101.

Smith, 1110 We
1947 Food of killifish and white porch in relation to
supply. J. Fish. Res. Ed. Can. 7(1); 22-54.

Surber, Eugene W.
1941 A quantitative study of the food of the smallmouth
black bass, (Micropterus dolomieu), in three eas-
tern streams. Trans. Am. Fish. Soc., 1940, 70:
511—554.

 

71

Surber, Eugene W.

1945

Swingle H.
1950

The effects of various fertilizers on plant growths
and their probable influence on the production of
smallmouth black bass in hard-water ponds. Trans.
Am. Fish. Soc., 1945, 75: 577-595.

S. and E. V. Smith
Management of farm fish ponds. Ala. Poly. Inst.
A331". Exp. Sta. Bull. 254, 1950: 1'05.

Titcomb, J. W., Cobb, E. W., Crowell, M. F. and C. M. McCay

1929

The relative value of plant and animal by-products
as feeds for brook trout and the basic nutritional
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carbohydrates, vitamines, inorganic elements, and
roughage. Trans. Am. Fish. Soc., 1929, 59:
126-145.

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