FACTORS INFLUENCING GROWTH AND SURVIVAL OF
WHITE SUCKER, Catostomus commersoni
by
Walter M. Koenst
Lloyd L. Smith, Jr. (Deceased)
Department of Entomology, Fisheries, and Wildlife
University of Minnesota
St. Paul, Minnesota 55108
Grant No. R804501
Project Officer
Kenneth E.F. Hokanson
U.S. Environmental Protection Agency
Monticello Ecological Research Station
Box 500
Monticello, Minnesota 55362
ENVIRONMENTAL RESEARCH LABORATORY.- DULUTH
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
DULUTH, MINNESOTA 55804
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DISCLAIMER
This report has been reviewed by the Environmental Research Laboratory 5-
Duluth, U.S. Environmental Protection Agency, and approved for publication. ;
f
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or recommendation
for use.
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ABSTRACT
Growth responses of the white sucker, Catostomus commersoni, were examined
in relation to the influence of temperature, body size, season, daylength,
light intensity, food ration level and food quality. Sucker growth was
maximum at a temperature range of 19-26°C, depending upon experimental condi-
tions. Fish reared under low light intensities grew an average 43% faster
than those reared under unshaded conditions. Growth on various diets was best
on live tubificid worms presented over sand substrate >tubificids (no soil
substrate) >frozen Daphnia >0regon Moist pellets >Glencoe Mills pellets. The
optimum temperature for growth on excess rations of live tubificids was 25 C
and was 19°C on restricted rations (1.5% fish body dry weight). Maximum
specific growth rate decreased nearly 4-fold over a size range of 12 to 175g,
but no difference in optimum temperatures were found. Fish of the same approx-
«
imate size grew twice the rate in the spring as compared to other times of the
year. Photoperiod showed little influence on growth rate, but fish exposed to
shorter daylength showed a marked increase in time to achieve a maximum growth
rate.
The ultimate upper incipient lethal temperature (UUILT), determined by
slowly increasing (0.5°C/day) acclimation temperature to death, was 32.5 C
for juvenile white suckers and 31.5°C for adults. The UUILT was 2-3°C higher
than the upper lethal temperatures measured by the classical approach involving
the direct transfer technique.
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CONTENTS
Abstract ; .' ii i
Figures v
Tables vi
1. Introduction 1
2. Conclusions and Recommendations 3
3. Materials and Methods 6
Experimental tanks and water supply 6
Experimental fish i 7
Fish food f:7
Proximate analysis I 8
Experimental procedures 9
4. Factors Influencing Growth 11
Preliminary observations 11
Temperature X body size ^6
Season X daylength |7
Ration size X temperature 21
•Body composition 27
5. Factors Influencing Survival 29
6. Implications for Thermal Criteria 31
References 36
IV
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FIGURES
Number Page
1 The relationship between body size and maximum growth rate of
white suckers in the spring and summer 18
2 Relation of growth rate and ration at 5 temperatures for
juvenile white suckers 23
3 The relation of maintenance, optimum and maximum rations to
temperature for juvenile white suckers 25
4 Temperature-growth relationships of white suckers at prescribed
ration levels of live tubificids expressed as a percent of the
fish dry body weight per day 26
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TABLES
Number Page
1 . Effect of current flow on growth of white suckers 12
2 Effect of temperature on growth rate of white suckers 13
3 Growth rate of white suckers at different temperatures and
light intensities 14
4 Growth of white suckers affected by diet quality 15
5 Effect of temperature and body size on growth of white suckers 16
6 Effect of season and^daylength on maximum growth of juvenile
white suckers at three prescribed temperatures 19
7 Effect of photoperiod and temperature on growth stanzas of
whi te suckers 20
8 The effect of temperature and ration size on growth and food
conversion efficiencies of the white sucker 22
9 The effect of temperature, ration, and season on body
constituents of juvenile white suckers fed live tubificid worms... 28
10 Upper lethal temperatures of white suckers of different sizes
measured by slow acclimation and direct transfer methods 30
VI
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SECTION 1
INTRODUCTION
Growth of fish is affected by many variables including temperature,
season, body size, and food quality and quantity. These factors influencing
growth have been investigated with various species of salmonids (Brown 1946;
Brett et al. 1969; Brett 1971 a, b; Shelbourn et al. 1973; Brett and Shelbourn
1975; Elliot 1975; Wurtsbaugh and Davis 1977). Mo studies have described the
thermal responsiveness of cool- and warm-water species throughout an annual
growth cycle.
The white sucker, Catostomus commersoni, is a widespread cool-water
species important as a forage and bait fish. Both growth response as well as
lethal limits are necessary criteria to identify thermal impact on the en-
vironment, to improve culture techniques for laboratory research and to
enhance the bait industry. McCormick et al. (1977) have shown that sucker
fry grow best at a temperature of 26.9°C and reported an upper incipient
lethal temperature of 30.5°C for swim-up larvae acclimated to 21.1 C. Brett
(1944) reported an ultimate upper incipient lethal temperature of 31.2°C for
juvenile white suckers using a direct transfer technique from an acclimation
temperature of 25°C. Hart (1947) indicated that the ultimate upper lethal
temperature for juvenile suckers was 29.3 C. Hokanson (1977) noted that the
upper incipient lethal temperature of a species may vary as much as 4 C.
Highest values of the ultimate upper incipient lethal temperatures occurred
for summer tests at the highest acclimation temperature increasing slowly to
1
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vthe lethal temperature.
The purpose of the present study was to investigate the growth and
mortality rates of juvenile and adult white sucker under different temperature
regimens as related to body size, season, daylength and ration level. Pre- j
liminary studies were conducted to determine conditions that maximize growth
prior to initiation of experimental studies. The upper lethal temperatures
of suckers of different sizes were estimated by the direct transfer method
-and by slowly raising the acclimation temperature 0.5 C/day until death
occurred.
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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
. The growth optimum and ultimate upper incipient lethal temperature (UUILT)
of a species are parameters used in derivation of summer temperature criteria
for aquatic life. The growth optimum varied from 19-26°C for juvenile white
suckers while the UUILT varied from 28.2 to 32.5°C depending on experimental
conditions.
Growth of fish was best when reared without any discernible current
flow.
Growth of fish reared under shaded conditions was increased by an average
of 43% over those reared under unshaded conditions.
Maximum growth was observed at25°Con excess rations (9.11% fish body
dry weight) and at 19°C on restricted rations (1.5%). Best growth was
. «
observed with live tubificid worms presented over a natural sand substrate.
Growth on various diets decreased in the following order: Tubificids (sand
substrate) >Tubificids (no soil substrate) >frozen Daphnia >0regon Moist
pellets >Glencoe Mills pellets. Maximum gross food conversion efficiency was
26% at 22°C and 3.0% ration level of tubificids.
Maximum specific growth rate decreased nearly 4-fold over a size range
of 12 to 175g. Optimum temperature for growth was not influenced over this
size range. The weight exponent (slope) for this size range was -0.45 which
decreased when smaller fish were included in the growth rate-body weight
relationship.
3
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Fish of a common size had a 2-fold increase in maximum growth rate in
spring compared to other seasons. There was no difference in growth rate
between summer and winter fish under a 15hL-9hD photoperiod. Maximum growth
in summer occurred at 26°C and at 24°C in winter and spring tests.
Daylength changes had no significant effect on maximum growth rate or
optimum temperature. However, attainment of maximum growth under test -t,
conditions was increased from 2 to 4 weeks when fish were reared under 15hL-
»9hD and 9hL-15hD photoperiods, respectively, in a winter test.
The highest UUILT (32.5°C) was achieved by slowly raising the test
temperature 0.5°C/day until death. This approach measured an UUILT that was
2-3 C higher than that measured by the classical approach involving the direct
transfer of fish from an acclimation temperature to a series of lethal levels.
The UUILT for newly hatched larvae, swim-up larvae, juvenile, and adults
were 28.2, 30.5, 32.5, and 31.5°C, respectively.
It is recommended that each investigator run a series of preliminary
tests to optimize culture conditions prior to measurement of the physiological
optima for each respective species. Better control of light intensity in
bioassays with nocturnal or deep-water organisms is especially encouraged.
Growth of white suckers on live tubificids should be compared to growth
on natural components in their diet including live Cladocera and macroinverte-
brates.
Future bioenergetic studies should cover a broader biokinetic range of
-*
temperatures to include the lower and upper limits of zero net growth.
The large variation in measurement of the physiological optima and UUILT
for one species herein suggests that temperature criteria data base be
critically appraised or revised before adaptation of any literature values
4
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vto field problems (ie. 316a demonstrations).
Field validation of the laboratory data base on temperature criteria is
needed to confirm the best test procedures.
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SECTION 3
MATERIALS AND METHODS
EXPERIMENTAL TANKS AND WATER SUPPLY
All tests were conducted in 210 x 54 x 54 cm fiberglass tanks where a
30 cm standpipe at the downstream end of the tank maintained a volume of
340 liters. The water in each experimental tank, representing one test
temperature, was supplied by its own head tank where dissolved oxygen and
temperature were regulated. Water temperature in the head tank was regulated
by either electrical immersion heaters as used by Smith and Koenst (1975) or
a thermostatically controlled solenoid valve which allowed hot water to flow
through a series of immersed stainless steel heating coils. Dissolved oxygen
concentration was maintained near air saturation in the head tanks with the
aid of airstones. An airstone also was placed in each experimental fish tank
. *
to increase the oxygen concentration and to prevent thermal statification.
Water flowed by gravity from the head tank through garden hose to a horizon-
tally placed polyvinyl chloride pipe with three constricted glass outlet tubes
placed equally apart above the tank. These glass tubes dispensed a continuous
flow of water into the fish tank at a rate of 1.8-2.0 1/min. The water supply
was from a deep well and was transported to the head tanKs through polyvinyl
chloride pipe. A comprehensive analysis of the well water was reported by
Smith et al. (1976). Temperature was measured daily with an immersion thenno-
memter graduated to 0.1°C. A 24-channel temperature recorder monitored
temperature variation at less precise levels. Daylength was maintained at a
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light-9h dark photoperiod during acclimation and testing unless otherwise
stated. Dissolved oxygen was measured twice weekly with the azide modification
of the Winkler method (APHA et al. 1971). Total alkalinity v/as determined
twice during each test. A weekly determination of pH was made with a pH meter.
Temperatures fluctuated slightly (standard deviations ranged from 0.04 to
0.12); pH ranged from 8.18 to 8.30; dissolved oxygen ranged between 78-922
air saturation; and total alkalinity averaged 235 mg/1 as CaCO.,.
EXPERIMENTAL FISH
All juvenile suckers were acquired from a bait dealer in Sherburne
County, Minnesota. Large juvenile suckers (140-200 g) were secured from the
same source, but after they had been maintained for one year in the ambient
temperature study channels of the Monti cello Ecological Research Station,
U.S. Environmental Protection Agency, Monticello, Minnesota. Adult suckers
(1000 g) were collected from Greenwood Lake, Cook County, Minnesota. Upon
arrival at the University of Minnesota Fisheries Laboratory, all fish were
given a routine prophylactic treatment of formalin plus malachite green
•
oxalate for 3 days as prescribed by the Committee on Methods for Toxicity Tests
with Aquatic Organisms (1975). Fish were kept in holding tanks at 11°C prior
to acclimation.
FISH FOOD .
Several types of food were given to the fish during holding and testing.
During the initial holding period, fish were fed frozen adult brine shrimp
(Artemia) and Oregon Moist pellets. Different types of food v/ere presented to
the suckers during the acclimation and testing period. During the initial
18 months of the study, Oregon Moist pellets (3/64) was primarily used for
growth tests. During the second phase, live tubificid worms were fed to the
7
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fish. Along with the food previously mentioned, Glencoe pellets (#1 granules)
and frozen adult Daphnia magna were also used in the specific food test.
An excess ration of Oregon Moist pellets was fed to the fish with the aid
of an automatic clock feeder. This method was useful in presenting the food1
continuously over a long period of time and especially in dispensing the food
at night during the white suckers' natural active feeding period.
Tubificid worms were collected from two sources: Raven Creek, Scott
County, Minnesota, and in a trout hatchery. They were held in a holding tank
with clean substrate and flowing water for several weeks prior to being fed to
the fish. Subsamples of worms were analyzed for body constituents and were
found to contain about 76% water, 7% fat, and 13% protein. Live worms were
placed in the fish tanks and, thus, were available for feeding 24 hours per
day. A fine granular sand substrate (1.5 cm deep) was placed in each experi-
mental tank to aid in the acceptance of tubificids as a food.
Daphnia were captured in Raven Creek, Scott County, Minnesota, which was
fed by an outfall from a sewage treatment pond. Daphnia were in abundance
during May and. June and large amounts were collected with drift nets in a
short time. They were immediately frozen with dry ice at capture and were
kept frozen until fed to the fish. Daphnia cubes were thawed and presented
to the fish at least twice daily.
PROXIMATE ANALYSIS
Half of the fish were frozen at the end of each experiment for determi-
nation of fat and protein content. Water content was determined from fresh
fish after each test and from frozen fish at a later date. Fish were oven-
dried at 105°C for 24h to determine percentage water content. Fat content
was determined from frozen samples which were oven-dried at 85 C to a constant
8
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^weight. The dried samples were crushed and extracted with n-hexane (Brett
et al. 1969). The residue remaining after fat-extraction was analyzed for
nitrogen content by the micro-KjeldahT technique for protein determination.
A factor of 6.25 was used to obtain the mean protein value. Subsamples of
tubifield worms were also analyzed for body constituents with the same
i
procedures.
EXPERIMENTAL PROCEDURES
Generalized procedures are described herein. Specific details of the
experimental design of each study will be described under the appropriate
section.
All fish were transferred from holding tanks to experimental tanks
within a period of 7 days after prophylactic treatment. Fish were randomly
assigned to a test tank after screening for a relatively uniform size. The
temperature was increased at a rate of l°C/day, and the fish were given an
additional acclimation period of 2 weeks to experimental tanks after the final
test temperature was reached.
To start the growth test, all fish were anesthetized with tricaine
methanesulfonate (MS-222) and cold-branded with "liquid nitrogen". The
branding was done with branding irons that were super cooled within a liquid
nitrogen bath. The numerical brand was placed dorsally above the base of the
pectoral fin. Fish were blotted with paper towels and weighed to the nearest
0.01 g and measured to the nearest mm during the marking procedures, and every
2 weeks throughout a 4- to 6-week growth period. Fish were fed daily during
acclimation and testing, and observations were made for mortality. Growth in
2-week intervals was expressed as a specific rate (percent change in weight/
time) after Brett et al. (1969). The specific growth rate is the slope of the
9
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regression of the natural leg of weight on time multiplied by 100. All data
were statistically examined to describe the optimum range by Analysis of
Variance followed by Duncan's New Multiple Range Test (Steele and Torrie
1960). The data was reported as specific growth rate + 2 standard errors.
The upper incipient lethal temperature (UILT) was determined by the
method of Fry (1947) whereby fish were transferred directly from a constant
acclimation temperature to a series of constant temperature baths bracketing
the median response. The incipient lethal temperature was defined by Fry as
the temperature beyond which 50 percent of the population cannot live for an
indefinite period of time. The UILT was established for acclimation
temperatures of 12, 16, 20, and 24° C as an initial range finding test. The
ultimate upper incipient lethal temperature (UUILT) is the highest UILT which
can be raised by thermal acclimation. The UUILT v/as determined by exposing
acclimated fish to a slow temperature rise (0.5 C/day) until death after
Cocking (1959) and Fry (1971). Percent survival and the corresponding mean
daily temperature in the preceeding and final 24h interval was used to
determine the temperature where 50 percent of the population would die by
«
graphical interpolation. The UUILT was determined for white suckers of
different sizes after a 4-week growth study for fish reared at constant
temperatures near optimum (26 and28°C). Feeding was terminated above 30°C
since it could influence the response to the upper lethal temperature.
10
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SECTION 4
FACTORS INFLUENCING GROWTH
PRELIMINARY OBSERVATIONS
During the first phase of the project, it became apparent that the white
sucker would not achieve maximum growth in the laboratory using methods that
have been previously demonstrated with other fish species. It was hypothesized
that sucker growth could be maximized by controlling variables such as
water current flow, temperature, light intensity, and diet quality. These
variables can maximize sucker growth by influencing food acceptance and/or
reducing their spontaneous activity and routine metabolism.
Water Current
Juvenile suckers placed in holding tanks did not readily accept pellet
food (Oregon Moist) but did feed readily on adult frozen brine shrimp. The
brine shrimp distributed more evenly in the tanks due to slight currents
created by airstones and the fresh water inflow. A test was initiated to
determine if current would enhance food acceptance. Water was circulated by
a pump in a circular tank to achieve the desired current. Fish were tested
under low light intensity (less than 5 ft-candles) at 22°C under both current
and non-current conditions. Fish living without water current grew nearly
twice the rate of fish living in a current (Table 1).
Temperature
A preliminary test was conducted to determine the optimum temperature for
11
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TABLE 1. EFFECT OF CURRENT FLOW ON GROWTH OF WHITE SUCKERS*
Current*
Non-current++
x Initial
wet wt. (g)
11.2
10.2
Specific growth
rate (%/day)
0.938
1.839
*Test conducted in summer at 22°C under a light intensity of less
than 5 ft-candles. All fish fed an excess ration of Oregon Moist
pellets.
+Water current was created by a pump in a circular tank to disperse
food pellets and transport them to fish. Flow rate and velocity
was not measured.
++Fish received a similar continuous flow of fresh water, but flow
was adjusted to avoid creating any discernible current.
growth of white suckers fed to satiation on Oregon Moist pellets. A growth
test was started with juvenile suckers (10 g) at eight different temperatures
ranging from 12° to 29°C (Table 2). Fish grew best at 24°C and had an optimum
temperature range of 20 to 25°C. Growth was significantly reduced above and
below this temperature range (P < 0.05).
Light Intensity
The current (Table 1) and temperature (Table 2) experiments indicate that
light intensity could be an important factor influencing growth. A comparison
of growth rates at 22°C between the two types of tests indicate that suckers
grew at a greater rate at low light intensity. It was observed by Stewart
(1926) and Campbell (1971) that white suckers normally feed during darkness.
Nocturnal activity was also noted by Spoor and Schloemer (1938) who found
suckers to move inshore during evening hours and offshore during morning hours
A growth test with 35 g suckers was initiated to investigate the effect of
12
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TABLE 2. EFFECT OF TEMPERATURE ON GROWTH RATE OF WHITE SUCKERS*
Temperature (C)
11.9
16.0
18.0
19.9
22.0
24.0
26.0
28.9
x Initial
. wet wt. (g)
10.72
11.01
10.74
10.93
10.93
10.63
10.41
9.91
Specific growth
rate (%/day)+
0.140 + 0.051
0.330 + 0.122
0.669 + 0.195
1.014 + 0.223
1.032 + 0.206
•1.070,+ 0.200
0.931 + 0.187
-0.032 + 0.332
*Tests conducted during fall at a light intensity of 11.5 ftr-candles.
Fish fed an excess ration of Oregon Moist pellets over a 42-day
period.
+Rate + 2 SE; N = 20 for each treatment.
light intensity. After a two-week acclimation period to test conditions, fish
were tested for growth for a tv/o-week period under unshaded conditions (11.5
ft-candles). This was followed by a two-week growth period where shade was
provided by placement of a black plastic cover over the lower two-thirds of
the water surface. Light was supplied by two 4fl-watt fluorescent bulbs (Vita-
Lite) providing a light intensity of 11.5 ft-candles in the unshaded portion
and 0 ft-candles in the shaded portion. Fish were always observed at the
lowest light intensity. Fish were tested at seven different temperatures
ranging from 14° to 26°C (Table 3). For all temperatures combined, growth
rate was increased by an average of 43% after shade was provided, even though
these fish were a larger initial size than in the unshaded* test. Growth rate
was significantly greater under shaded conditions (P < 0.05). The unshaded
test showed 22°C to be the optimum temperature for growth as compared to all
other temperatures (P < 0.05), while the shaded test showed an optimum tempera-
ture of 24°C and an optimum temperature range of 18°C to 26°C (P < 0.05).
13
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TABLE 3. 'GROWTH RATE OF WHITE SUCKERS AT DIFFERENT TEMPERATURES
AND LIGHT INTENSITIES*
Temperature (C)
14.0
16.0
18.0
20.0
21.9
24.0
26.0
x Initial
wet wt. (g)
37.48
35.30
34.28
35.39
34.19
34.43
33.57
Specific growth rate
(%/day)+
Unshaded-H- Shaded+++
0.34 + 0.14 0.63 + 0.26
0.52 + 0.20 0.73 + 0.21
0.67 + 0.22 1.05 + 0.27
0.79 + 0.23 0.82 + 0.24
1.22 + 0.31 1.40 + 0.35
0.87 + 0.28 1.48 + 0.34
0.87 + 0.17 1.13 + 0.26
*Fish tested in winter and fed an excess ration of Oregon Hoist pellets.
+Rate + 2 SE for N = 10 for each treatment.
++11.5 ft-candles.
+++0 ft-candles underneath shaded portion of tank (lower two-thirds area), .
and 11.5 ft-candles at upper end (one-third area).
Eisler (1957) concluded that high light conditions stimulated growth of
chinook salmon fry. Conversely, suckers are nocturnal feeders and could be
stimulated by low light conditions.
Diet Quality
It was thought food type could still be a significant limiting factor in
achieving maximum growth rate (Brett 1971b). Furthermore, the amount of
Oregon Moist consumed by the suckers would be difficult to quantify over time.
Live food would be preferable in food ration tests. Tests were conducted to
determine food type most suitable in obtaining maximum growth rates. The
presence of a substrate with live food was also tested as a factor influencing
growth or food acceptability. Juvenile suckers were tested for a two-week
growth period at 22°C after a two-week acclimation period. Foods tested were
14
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TABLE 4. GROWTH OF WHITE SUCKERS AFFECTED BY DIET QUALITY-
Specific growth rate
Food
Live tubi field worms 4.33
(sand substrate)+
Live tubificid worms 3.30
(no substrate)
Frozen Daphm'a 3.19
Oregon Moist 1.78
GTencoe Mills -0.03
*Test conducted in spring at low light intensity (0 ft-candles
under lower two-thirds tank) at 22 C. Initial wet weight
was 10-11 g.
+A 1.5 cm layer of fine sand distributed evenly over bottom of
tank.
Oregon Moist pellets, Glencoe pellets, frozen adult Daphm'a and tubificid
worms. The tubificids were presented as two treatments, one being a tank
with no substrate and the other being a tank with a sand bottom. All fish
were fed to sa'tiation. Fish fed live tubificids over a sand substrate had a
maximum growth rate of 4.3%/day (Table 4). Growth declined in decreasing
order from tubificids (sand substrate) > tubificids (no soil substrate) >
frozen Daphm'a > Oregon Moist > Glencoe Mills.
As a result of the preliminary tests, culture techniques enhancing growth
were incorporated into subsequent experimental procedures- All experiments
v/ere conducted under low light intensity (11.5 ft-candles at upper one-third
tank; 0 ft-candles under shade cover over lower two-thirds tank), fish were
fed live tubificid worms, and a sand substrate was provided for feeding.
A continuous flow-through (1.8-2.0 1/min) with no current.was provided in the
test chambers. These improvements in sucker culture increased growth rates
15
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TABLE 5. EFFECT OF TEMPERATURE AND BODY SIZE ON GROWTH OF WHITE
SUCKERS*
x Initial
wet wt. (g)
11.79
10.79
11.73
10.71
12.61
12.29
11.96
166.39
161.54
172.96
161.67
175.06
157.31
H
10
10
10
10
10
10
10
5
5
5
5
5
5
Temperature
12.1
17.0
20.9
24.0
25.9
28.1
29.9
12.1
17.0
21.0
24.0
26.1
28.0
Specific growth
rate (%/day)+
0.05 + 0.05
0.55 + 0.22
1.79 + 0.25
1.80 + 0.30
2.37 + 0.27
1.33 + 0.39
0.20 + 0.21
0.40 + 0.08
1 O.S8}+ 0.06
' 0754 + 0.08
0.65 + 0.15
0.68 + 0.14
0.24 + 0.09
*A summer test at low light intensity. Fish fed an excess of live
tubificid worms.
+Rate + 2 SE.
more than four-fold to a level that approximates growth rates observed under
field conditions at low fish density (K.E.F. Hokanson, U.S. EPA, Monticello
MN, personal communication). Mortality of fish was also negligible at all
temperatures herein when growth conditions were optimized.
TEMPERATURE X BODY SIZE
The effect of body size of white suckers on growth rates were tested at
excess rations of live tubificid worms at different temperatures during the
summer. Two sizes of juvenile white suckers were tested (Table 5). Fish of
both sizes showed an optimum temperature range for growth to be 21-26 C
(P < 0.05). Maximum growth occurred at 25°C where the 12.6 g fish grew at a
rate of 2.37%/day and the 175.1 g fish grew 0.68%/day. Juvenile suckers
(mean wet wt. 25.6 g) tested at excess rations at 25°C grew at a maximum rate
of 1.38%/day (see Ration Size X Temperature section, Table 8).
15
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Brett and Shelbourn (1975) found that a log-log transformation provides
a good linear relationship between maximum growth rate and body weight for
salrconids. A Similar relationship exists for juvenile white suckers (Fig. 1).
The maximum growth rate relationship for white suckers fed excess rations at
26 C for a weight range of 12.6-175.1 g was expressed by the linearized
equation:
InG = 1.9160 - 0.4523 InW (1)
where G = specific growth rate (%/day)
W = initial wet weight (g)
2
The fitted regression line between the summer data points had an R value of
0.967.
Suckers tested in the springtime showed a higher growth rate than at
other seasons for similar sized fish (see Season X Daylength section, Table 6).
The maximum growth rate - body weight relationship (10.1-53.6 g) was derived
only for comparative purposes by the linearized equation:
InG = 2.3541 - 0.3391 InW (2)
Caution should be exercised in extrapolation of these data beyond the indicated
size range as inclusion of smaller fish will reduce the size correction factor
(slope) further. McCormick et al. (1977) observed a maximum specific growth
rate of 14.8%/day for white sucker larvae with an initial wet weight of 4.1 mg.
Addition of this data point to the spring growth rate-body weight relationship
2
would give a slope of -0.168 with an R = 0.972.
»
SEASON X DAYLENGTH
The effect of season and daylength on sucker growth was investigated.
Fish were compared for growth at three different times.of the year (spring,
summer, and winter) and at three different temperatures (24, 26, and 28C) at
17
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20 40 60 80 100
BODY WEIGHT (G)
200
Figure 1. The relationship between initial body size and
maximum growth rate of white suckers in the spring
and summer.
at a 15h L-9h D photoperiod. Because of a possible effec't of season and
daylength on growth rate, winter fish were tested at tv/o photoperiods: 15h L-
9h D, and 9h L-15h D.
The time of year had a marked effect on grov/th rates of suckers. Fish
during late spring (May-June) displayed nearly a two-fold increase in growth
18
-------
TABLE 6. EFFECT OF SEASON AND DAYLEMGTH ON MAXIMUM GROWTH OF JUVENILE WHITE
SUCKERS AT THREE PRESCRIBED TEMPERATURES*
Photoperiod
Season h-L/h-D
Spring++
Summer++
Winter++
15/9
15/9
15/9
15/9
15/9
15/9
15/9
15/9
15/9
15/9
15/9
15/9
9/15
9/15
9/15
x Initial
wet wt. (g)
10.14
9.97
9.50
53.56
55.00
51.47
10.71
12.61
12.29
11.66
11.17
11.17
12.13
1-1.41
11.40
Temperature
(C)
24.0
25.0
28.0
24.0
26.1
28.0
24.0
25.9
28.1
24.0
26.0
28.0
24.1
26.0
27.9
Specific growth
rate (%/day)+
4.80 + 0.41
4.35 + 0.43
2.89 + 0.34
2.73 + 0.22
2.60 + 0.18
1.56 + 0.26
1.80 + 0.30
2.37 + 0.27
1.33 + 0.39
2.39 + 0.26
2.33 + 0.22
1.67 + 0.34
2.71 + 0.29
2.60 + 0.28
1.78 + 0.24
*Fish fed an excess ration of live tubificid worms at low light intensity.
+Rate + 2 SE for N = 20.
++28 day growth test began in late May, late July, and early January,
respectively.
rate compared to growth during summer and winter (Table 6, Fig. 1). Large
juvenile suckers (54 g) displayed a greater growth rate (2.73%/day at 24°C)
in the spring than did smaller 11 g individuals (1.80%/day at 24°C) in the
summer. The optimum temperature for growth on excess rations was 26°C in
summer and was reduced to 24 C in winter and spring tests, although growth
rates were not significantly different (P > 0.05). Fish (10-12 g) showed no
significant differences in growth rate between summer and winter seasons for
a 15h L-9h D photoperiod.
One phenomenon brought out by the winter test was that photoperiod played
an important part in the acclimation rate to test conditions based on
19
-------
TABLE 7. EFFECT OF PHOTOPERIOD AMD TEMPERATURE ON GROWTH STANZAS
OF WHITE SUCKERS*
Specific growth rates (%/day)
Photoperiod
Temperature
(C) 15h L - 9h D 9h L - 15h D
j+ JJ_++ ! II
24 2.37 2.40 1.46 2.71
26 2.34 2.33 1.85 2.60
28 1.74 1.59 1.14 1.78
*Fish fed an excess of live tubificid worms at low light intensity
in winter.
+Period I - first two-week period of growth test, following an
initial 12-day acclimation period to test tanks, temperature,
and photoperiod.
++Period II - second two-week period of growth test.
maximum growth potential. All fish prior to acclimation and testing were
treated alike and were exposed to a short daylength during holding. Upon
placement in their respective tanks, the photoperiod was changed over a period
of three days, fish were acclimated to test temperatures at a rate of 1 C/day,
and held for two weeks before the growth test began.
Results showed that fish acclimated to their test conditions at a slower
rate when exposed to decreased daylight (Table 7). Based on maximum growth
rate, it took over four weeks for the fish to be fully acclimated to their
test conditions during shorter daylength hours compared to'two weeks acclima-
tion at the longer daylength. No differences in growth rates were noted
between the first two weeks and the second two weeks of the 15h L-9h D photo-
period (P > 0.05). Conversely, suckers exposed to the 9h L-15h D photoperiod
showed nearly a two-fold increase in growth between Period- I and II (P < 0.05)
20
-------
Although no significant differences in growth rates were found due to photo-
period based on the last two weeks of the test (P > 0.05), there was a large
difference in growth rate between suckers exposed to the two photoperiods for
the first two weeks of. the. test (P < 0.05). Special precautions are needed
to insure complete acclimation to test conditions if "aseasonal" growth
studies are to be conducted'in winter.
RATION SIZE X TEMPERATURE
Growth tests were conducted on white suckers (mean wet wt. 29 g) at
different temperatures and reduced ration levels of live tubificid worms.
Fish were tested at five different temperatures (16, 19, 22, 25, and 28°C)
and five daily ration levels (0, 1.5, 3.0, 4.5%, and excess). The restricted
ration was prescribed at the start of each two-week growth period and was based
on estimated mean dry weights of fish at the mid-point of each interval.
Mean dry weight was estimated from final weight (initial weight of current
interval) and specific growth rate in the previous two-week interval). Sub-
sequently, fish received a slightly higher portion of feed than the prescribed
ration in the- first week and a slightly lower portion in the latter week of
the growth interval. Tubifex were weighed wet and fed daily to the fish.
Subsamples of tubificid worms and fish were dried and weighed at the end of
the study. Measured specific growth rates were used to estimate daily mean
fish wet weights. These estimated fish wet weights and measured food wet
weights were converted to dry weights to determine actual ration size per day.
9
These measured ration sizes, test temperatures, and corresponding growth rates
are reported in Table 8. Fish at 16°C did not consume their prescribed ration
of 1.5% equally. Because half of the fish consumed little food, the mean
growth rate (0.047%/day) was lower than expected while feeding fish grew at
21
-------
TABLE 3. THE EFFECT OF TEMPERATURE AMD RATION SIZE ON GROWTH AMD FOOD CONVERSION
EFFICIENCIES OF THE WHITE SUCKER*
Temperature Ration sizes
(C) (% dry wt. food/
dry wt. fish/.
day)
16.1
16.1
16.2
16.0
19.0
18.9
19.0
19.2
22.0
22.0
22.0
22.1
25.0
24.9
24.8
25.0
25.1
28.1
28.1
28.0
27.8
28.0
0
1
2
3
0
1
2
4
0
1
3
4
0
1
3
4
9
0
1
3
4
10
•
.55
.89(3.10)+
.05(4.51)
.45
.96
.22(4.60)
.55
.03
.65
.46
.04
.63
.ll(Excess)
.52
.08
.50
.92(Excess)
x Initial Specific
wet wt. growth rate
(g) U/day)
28
30
23
25
30
28
23
27
31
31
28
26
31
30
31
25
25
33
32
31
28
25
.1
.4
'.6
.9
.1
.9
.4
.6
.3
.6
.0
.5
.8
.5
.8
.4
.6
.4
.3
.1
.4
.2
-0
0
0
0
-0
0
0
0
-0
0
0
0
-0
0
0
1
1
-0
0
0
0
0
.25 +
.05 +
.47 +
.43 +
.28 +
.26 +
.66 +
.72 +
.34 +
.24 +
.80 +
.89 +
.53 +
.16 +
.67 +
.02 +
.38 +
.62 +
.12 +
.65 +
.81 +
.91 +
.04
.44
.13
.20
.09
.11
.18
.25
.07
.14
.20
.23
.09
.09
.12
.23
.20
.09
.07
.20
.21
.21
Gross
conversion
efficiency
(*)
3
16
14
17
22
17
15
26
19
11
21
22
15
7
21
17
8
.0
.2
.1
.9
.4
.1
.2
.4
.2
.0
.9
.0
.2
.8
.0
.9
.3
Net 1
conversion
efficiency
(%)
4
18
16
32
28
20
36
37
23
44
34
28
17
43
35
24
9
.1
.8
.2
.4
.7
.2
.2
.6
.8
.4
.3
.9
.3
.7
.4
.8
.4
*A summer test at low light intensity. Fish were fed live tubificid worms.
+Ration sizes in parenthesis were the prescribed ration but were not fully
consumed.
»
a rate of 0.385%/day. Therefore, this data point was smoothed out in subsequent
plots.
Growth rate was plotted against ration for each temperature (Fig. 2),
resulting in curves that described maintenance ration, optimum ration, and
maximum ration. These growth parameters can be derived geometrically from the
22
-------
..10*
-1.0
RATION (% WEIGHT/DAY)
Figure 2. Relation of growth rate and ration at 5 temperatures
for juvenile white suckers. Dashed lines indicate
gross conversion efficiencies.
grov/th rate-ration size curve (Thompson 1941; Brett et al . 1969). The
maintenance ration, the ration where fish maintains its weight without gain
or loss, occurs where the line crosses the zero growth rate axis. The optimum
ration, the ration where greatest growth occurs for the least intake, can be
derived by drawing a tangent from the origin (0% growth rate and 0" ration) to
the curve. The maximum ration, the ration that provides maximum growth,
occurs at the asymptote of the curve.
The relation of maintenance, optimum and maximum ration to temperature
23
-------
for white suckers, derived from the procedure described above, are shown in
Fig. 3. The rations describing these three growth parameters increased with
an increase in temperature, but both maximum ration and optimum ration decreased
at temperatures higher than- 25°C. At 28°C, both the maximum and optimum
ration decreased due to a lower efficiency of food conversion (Table 8).
The optimum temperature for growth decreased as the ration size decreased.
Growth rate was plotted against temperature for each specific ration level
(Fig. 4). Each curve describes the scope for growth for fish (25-30 g) on a
prescribed ration during the summer and early fall. A greater growth
potential would be expected in the spring. Maximum growth rate was at 25 C
on excess rations and decreased to 19 C at a 1.5% ration level. Weight loss
of unfed fish increased exponentially with increased temperatures. Zero
growth limits of juvenile white sucker were estimated by graphical extrapola-
tion. Lower and upper limits were 9 and 30 C, respectively, which were similar
to those observed in larvae (McCormick et al . 1977). Broken lines were drawn
by eye to these graphical limits. •.
Gross food conversion efficiency (E ) provides a useful index of the
efficiency of white suckers to convert food into fish flesh. With a common
unit of dry weight, this index was calculated using the following equation:
E = T X 100 (3)
9 1
where G = growth
I = food intake
*
Highest conversion efficiency for each temperature occurred in the area of
most rapid change in curvature (Fig. 2). The maximum gross efficiency (26%)
occurred at 22°C on a restricted ration of 3.0% (Table 8). Gross efficiency
v/as generally less than 15% at all ration levels below 15°C and at lower and
higher ration levels above 25 C.
24
-------
I
g s
UJ
z 4
g
K-
£C 3
\
MAXIMUM RATION
= -7.330+-0.610X
OPTIMUM RATION
Y = -15.477 + 13.729 LOQ
R2=.B«2
10'
MAINTENANCE RATION
Y= -4.264 + 3.833 LOQ,0X
R2=.8S5
16 18 20 22 24
TEMPERATURE (C)
26
28
Figure 3. The relation of maintenance, optimum, and maximum
rations to temperature for juvenile white suckers.
Solid line fitted by regression equation, broken
line fitted by eye.
The daily maintenance ration (M), obtained from Fig. 3, can be subtracted
from the food intake to determine net conversion efficiency (E ). This index
measures the efficiency of utilization of the fraction of food available for
grov/th and it can be derived with the following equation:
E =
n I-M
25
X 100
(4)
-------
>
<
o
g
ui
£
UJ
i-
cc
I
O
cc
a
o
u.
O
UJ
Q.
CO
1.0
O.B
0.6
0.2
0.0
-0.2
-0.4
-0.6
-O.B
1
18 21 24 27
TEMPERATURE (C)
30
Figure 4. Temperature-growth relationships of white suckers
at prescribed ration levels of live tubificids expressed
as a percent of the fish dry body weight per day.
Shaded area is the zone of thermal resistance in excess
of the ultimate upper incipient lethal temperature of
32.5°C.
»
Highest net efficiency occurred at the combination of higher temperatures and
lower rations. The maximum net efficiency (44.4%) occurred at a ration size
of 1.46% at 25°C. In this example, the actual ration resulting in a growth
rate above the maintenance level was 0.36% where fish grew at a rate of
0.160%/day.
26
-------
BODY COMPOSITION
Changes in body composition were examined to determine how temperature
and food intake influence the percentage of water, fat, and protein (Table 9).
Samples of fish fed ration levels of live tubificids at 0, 1.5, and 3.0% were
examined at the end of the test. No noticeable changes in protein and
moisture contents were found between different temperatures and ration sizes.
Fat content increased with an increase of food intake, particularly at
temperatures of 19°C and below.
Fish that showed a high growth rate during the spring were also analyzed
for body composition. These fish demonstrated a much greater food intake and
growth potential during this time of year. These fish were compared to fish
fed a ration of 3%/day which ^v/as close to the optimum ration level for their
respective temperatures (Fig. 3). No change was noted in percentage protein
and water, but fat content was significantly increased over summer fish
(P < 0.05).
27
-------
-TABLE 9. THE EFFECT OF TEMPERATURE, RATION, AND SEASON ON BODY CONSTITUENTS
OF JUVENILE WHITE SUCKERS FED LIVE TUBIFICID WORMS*
Ration
(% dry weight)
0.0
0.0
-o.o
0.0
0.0
1.5
1.5
1.5
1.5
1.5
3.0
3.0
3.0
3.0
3.0
Maximum
Maximum
Maximum
Nominal
Temperature
16
19
22
25
28
16
19
22
25
28
16 .
19
22
25
28
24
26
28
x Water*
(C) (%)
SUMMER FISH+++
75.2
78.2
78.0
78.2
76.8
77.8
76.1
76.5
77.7
76.2
76.3
76.5
76.4
75.5
76.4
SPRING FISH2
75.0
75.7
75.9
x Fat++
(*)
4.8
2.3
2.3
2.2
2.4
3.0
3.9
3.8
3.0
3.1
4.6
4.5
4.0
3.7
3.6
7.4
6.0
6.6
x Protein-H-
(%)
11.9
13.4
13.5
13.0
12.3
14.0
14.3
14.7
14.0
14.2
14.3
14.2
15.0
14.3
13.7
12.8
13.4
13.2
*Tubificids contained 84.5% water, 2.3% fat, and 7.4% protein.
+N - 10.
++N =5.
+++From ration size X temperature test (Table 8).
£From season X daylength test (Table 6); initial size 10 g'.
28
-------
SECTION 5
FACTORS INFLUENCING SURVIVAL
For many years the standardized procedure for determining the upper
lethal temperature was to subject fish to a sharp increase in temperature,
usually done by a direct transfer technique from an acclimation temperature to
a series of upper lethal temperatures. Many field reports have shown fish to
survive temperatures higher than the reported UILT determined in laboratory
studies (K.E.F. Hokanson, U.S. EPA, Monticello, MM, personal communications;
Wrenn and Forsythe, 1978). It was hypothesized that the direct transfer
technique under estimates the UUILT because it does not maximize the acclima-
tion temperature and provides additional stress to the fish from handling.
Theoretically, slow rates of thermal increase (< 1 C/day) that maximize
acclimation temperature and minimize handling stress should give the highest
•
estimate of the UUILT.
Upper lethal temperatures were determined by both the direct transfer
technique and the slow temperature rise for white suckers of different sizes
(Table 10). The UUILT for smaller juveniles (19.7-34.5 g) was 32.2 to 32.5°C
and was 31.3 to 31.7°C for larger juveniles (168-192 g) and adults. Uhite
suckers exposed to a slower rise in temperature experienced* death (50%) at a
temperature that is approximately 2 C higher than suckers tested with the
direct transfer technique and by Brett (1944), and 3°C higher than the
previously reported UILT by Hart (1947).
29
-------
TABLE 10. UPPER LETHAL TEMPERATURES OF WHITE SUCKERS OF DIFFERENT SIZES
MEASURED BY SLOW ACCLIMATION AND DIRECT TRANSFER METHODS*
x wet
wt. (g)
Acclimation
temperature (C)
Upper lethal
temperature (C)
Source
Ultimate Upper Incipient Lethal Temperature +
Present study
7
7
.5
26.
19.
34
30.9
191.8
168.7
1000
26.1
28.0
26.0
28.0
26.1
28.0
23.0
32.4
32.2
32.5
32.3
31.3
31.7
31.5
Upper Incipient Lethal Temperature ++
12-15
12-15
12-15
12-15
2-20
juvenile
*
12.0
16.1
20.2
24.1
25
25-26
28
30
30
30
29
31
.6
.3
.5
.5
.3
.2
(96-h)
(133-h)
(12-h)
n
n
n
ii
Hart,
Brett
n
n
n
n
1947
, 1944
*Tests conducted in summer at low light intensity
+Initial acclimation temperature increased 0.5C/day until death. Fish not
handled before test as routinely done in direct transfer technique. Fish
were not fed above 30°C.
++Direct transfer of fish from an acclimation tank to a series of lethal
temperature baths.
30
-------
SECTION 6
IMPLICATIONS FOR THERMAL CRITERIA
, The physiological or growth optimum and UUILT of a species are used
directly in derivation of summer limiting temperatures for aquatic life (U.S.
EPA, 1976). These thermal criteria endpoints can be modified by several
variables which greatly influence bioassay results and thermal responsiveness
under field conditions. The light intensity threshold must be carefully
controlled to provide optimal culture conditions and enhance the scope for
growth for nocturnal organisms. Slower rates of temperature increase that
minimize fish handling and maximize acclimation temperature give the highest
UUILT. Therefore, laboratory methodology must be critically appraised before
thermal criteria values are proposed or used. For some fish species, the
growth optima and UUILT may be underestimated and should be revised by first
recognizing sources of error as demonstrated herein.
Maximum growth of juvenile white suckers occurred over a wide temperature
range of 19 to 26°C, depending upon several variables. Ration level and diet
quality had the greatest influence on specific growth rate and optimum
temperatures, whereas season and light intensity had a lesser but significant
influence on these growth responses. Body size primarily'influenced maximum
specific growth rate and daylength primarily influenced acclimation time to
test conditions. Sucker larvae showed a similar growth response with an
optimum temperature range of 23.9 to 26.9°C (McCormick et a'l . 1979). The
best culture conditions produced an optimum near 26 C in this species. Lower
31
-------
growth optima would most likely be observed in nature where ration size is
usually restricted.
Maximum growth at optimum temperatures decreased nearly four-fold over a
size range of 12 to 175 g.- Optimum temperature for growth was not influenced
over this fish size range. The slope for the summer maximum growth rate-body
weight relationship was -0.452. The determined slope value compares favorably
with-salmonid growth-body weight relationships. Brett and Shelbourn (1975)
found that juvenile sockeye salmon (Oncorhyncus nerka) displayed a similar
slope of -0.416, but with higher intercept for a weight range of 2-40 g.
Their comparison with other investigations showed that the slope value of
-0.4 + 0.04 appeared to characterize the salmonid family. The slope value
declined to -0.168 by inclusion of larval white suckers in the spring growth
rate-body weight relationship. This suggests that these weight correction
factors are constant only for a limited size range and/or life history period.
Season had a marked effect on maximum growth of the white sucker indepen-
dent of daylength changes. White sucker of a common size had a two-fold
increase in maximum growth rate in spring compared to other seasons. Maximum
growth rate in summer occurred at 26°C and at 24 C in winter and spring tests.
There was no difference in growth rate between summer and winter fish under a
constant 15h L-9h D photoperiod. Swift (1955) found that growth of hatchery
brown trout, Salmo trutta, increased in the spring while temperatures were
still cold and decreased in autumn when temperatures were still warm. These
changes occurred despite the fact that they were fed to satiation. The
increase in growth in the spring has been correlated with increasing daylength
which stimulates endocrine activity including the production of growth hormones
(STH), while decrease in growth in autumn was related to gonadal maturation
(Brett 1979). Hogman (1968) also noted that seasonal changes in growth rate
32
-------
.of lake whitefish, Coregonus clupeaformis, was more closely related to daylength
than to changes in partially controlled water temperature.
Daylength changes itself did not influence maximum growth rate or optimum
temperatures in the white sucker. This is consistent with the observation that
low light intensity stimulates feeding and growth in this nocturnal species.
Reduced daylength, however, increased acclimation time to test conditions which
has important implications in the design of "aseasonal" growth studies. Clarke
et al. (1978) observed that sensitivity of salmonid fry to photoperiod varied
seasonally. Gross et al. (1963) found photoperiod to affect growth of green
sunfish, Lepomis cyanellus, but also noted that prior photoperiod history was
important. Brett (1979) stated that for freshwater fish, that long daylength,
especially increasing daylength applied over a number of months in the right
season, is stimulating to growth. The observed.effects on growth are not
large. Decreasing daylengths have an inhibiting effect on some freshwater
fish. Growth of nocturnal species such as walleye, Stizostedion vitreum, is
relatively more temperature dependent, while growth of diurnal species such as
yellow perch, .Perca flavescens, is relatively more photoperiod-dependent (Huh
et al. 1976). The lack of greater induced response by photoperiod, compared
with natural seasonal effects on normal populations (independent of temperature
effects), suggests the evidence for an endogenous annual rhythm which is not
subject to displacement by artificial control of daylength.
The loss of condition of winter fish and endogenous hormonal cycles nay
f
stimulate increased feeding to restore body food reserves. The growth rate of
white sucker increased in spring due to a large increase in food consumption.
Starvation alone is a normal endogenous stimulus to feeding activity. There-
fore, it is possible for suckers to increase their growth rate without
appreciable changes in food conversion efficiency or even with a possible
33
-------
decrease in efficiency. Wurtsbaugh and Davis (1977) indicated that rainbow
trout, Salmo gairdneri, were less efficient in food utilization for growth in
the spring. The increased growth in spring in suckers, consisted of a large
increase in relative fat content compared to other seasons. Fat deposition
of accumulation can occur rapidly in fish in response to enhanced feeding
activity, and can also be rapidly depleted on demand by other metabolic
processes and by overwintering (Shulman 1974). Although no fat analyses were
done on fish prior to testing, it was observed that fish at this time of year
were in relatively poorer condition at the start of the study than at other
times of the year.
The specific growth rate of the white sucker of a given size and season
is dependent mainly on the quantity of food consumed and temperature.
Increasing temperatures markedly increased the maximum ration, optimum ration,
and maintenance ration, but at temperatures above 26°C, both the optimum
ration and maximum ration decreased. This decrease was probably due to a
lack of appetite and the increase in maintenance requirements, and lower food
conversion efficiency. Maximum gross food conversion efficiency for white
suckers was 26% at 22 C and 3% ration level which compares favorably with
salmonids. Increasing temperatures also reduced gross efficiencies at low
ration levels (1.5%), while little effect was noted at higher ration levels.
This pattern was also found for rainbow trout (Wurtsbaugh and Davis 1977) and
for sockeye salmon (Brett et al. 1969).
Slow increases in temperature that maximize acclimation temperature
without handling fish has significantly increased previous estimates of the
UUILT. Juvenile and adult suckers tolerated temperatures 32.5° and 31.5 C,
respectively. The UILT for juvenile white suckers in this 96-h summer test
was 30.5°C. Brett (1944) reported an UILT of 31.2°C in a shorter 12-h
34
-------
summer test. A time period of at least 72-h is required to measure an UILT
(Brett 1970). Hart (1947) measured an UILT of 29.3°C for juvenile suckers
acclimated to 25°C in a winter test. The UILT of newly hatched and free-
swimming larvae were 28.2 and 30.5°C> respectively (McCorrnick et al. 1977).
These previously reported limits were based on tests where fish were subjected
to a very quick temperature change. When fish were exposed to a slower
temperature increase, an UUILT endpoint that was 2-3°C higher than the UILT
was attained for juvenile fish. This method avoids handling stress and
maximizes acclimation temperature. This method gives a more realistic upper
lethal limit when compared to field situations where fish have been observed
at temperatures higher than the upper lethal temperatures previously reported
in the literature.
35
-------
REFERENCES
American Public Health Association, American Water Works Association, Water
Pollution Control Federation. 1971. Standard Methods for the
Examination of Water and Wastewater. 13th ed. APHA, Washington, D.C.
-874 pp.
Brett, J.R. 1944. Some lethal temperature relations of Algonquin Park fishes.
Univ. Toronto Stud. Biol. Ser. No. 52, Pub! . Ontario Fish. Res. Lab.
No. 63, 49 pp.
Brett, J.R. 1970. Temperature. Animals. Fishes, pp. 515-560. In: 0. Kinne
(ed.). Marine Ecology. Vol. I. Environmental factors. Wiley-Interscience,
New York.
Brett, J.R. 1971a. Satiation time, appetite and maximum food intake of
sockeye salmon (Oncorhynchus nerka). J. Fish. Res. Bd. Canada 28: 409-415.
Brett, J.R. 1971b. Growth responses of young sockeye salmon (Oncorhynchus
nerka) to different diets and planes of nutrition. J. Fish. Res. Bd.
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Walter M. Koenst is self employed and can be reached for specific comments on
the manuscript at his home address.
1246 Seminary Ave
St. Paul, Minn. 55104
Dr. Lloyd L. Smith, Jr. was professor of fisheries, Dept. of Entomology,
Fisheries, and Wildlife, University of Minnesota, and was the original
principal investigator. He met an untimely death in June, 1978 before
completion of this grant.
Dr. Milton W. Weller, professor and head, Dept. Ent., Fish. & Wildlife was the
principal investigator at the conclusion of this grant. Reprint requests
can be mailed directly to him or the EPA project officer.
Dr. Kenneth E.F. Hokanson is the EPA Project Officer and can be contacted for
information about this report or the EPA thermal program.
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