University of Wisconsin-Milwaukee, Centerfor Great Lakes Studies. 600 East ... Maximum daily consumption rates of bloater Coregonus hoyi from Lake Michigan.
Transactions of the American Fisheries Society 123:335-343, 1994 © Copyright by the American Fisheries Society 1994
Maximum Daily Ration of Great Lakes Bloater FRED P . BINKOWSKI
University of Wisconsin-Milwaukee, Center for Great Lakes Studies 600 East Greenfield Avenue, Milwaukee, Wisconsin 53204, USA LARS G . RUDSTAM
Department of Natural Resources, Cornell Biological Field Station 900 Shackelton Point Road, Bridgeport, New York 13030-9750, USA Abstract .-Maximum daily consumption rates of bloater Coregonus hoyi from Lake Michigan were measured in the laboratory for 1-, 5-, 10-, 25-, 50-, 100-, and 200-g fish at 4, 8, 12, and 16ºC . These represent most of the ranges in bloater size and temperature likely to be encountered in Lake Michigan . Bloaters were raised from eggs in the laboratory and acclimated to test temperatures for 22-23 d prior to the experiments . Maximum daily consumption rates were determined by feeding the fish surplus amounts of brine shrimp Artemia sp. at 4-h intervals for 24 h. Specific daily ration increased with temperature up to 16°C for all size-groups . At 12 and 16ºC, the maximum daily ration of small bloaters (about 1 g) exceeded 120% of body weight per day (based on wet weight ; equivalent to 79%/d based on dry weight) ; the maximum daily ration of large bloaters (over 100 g) ranged between 5 and 12%/d (2-7%/d based on dry weight). As percentage of maximum consumption at 16°C, consumption rates averaged 82% at 12°C, 45% at 8ºC, and 28% at 4°C. These results can be described by the equation: CmaX = 1 .61 " W -0.538"F(T), where CmaX is specific maximum consumption rate (g g-1 d-1 ), Wis fish weight (g), and F(T) is a domeshaped temperature dependence function with an optimum temperature of 16 .8ºC (R 2 = 0.957, N = 27). Knowledge of maximum daily rations of fish is important for several reasons. The maximum ration represents the physiological upper limit for fish consumption, which is the limit for fish feeding in dense food aggregations and during periods of overabundant food supply . This limit is set by digestion rates rather than by the animal's ability to detect and capture prey . Maximum ration is a species-specific function of temperature and fish size (Brett 1971 ; Elliott 1975a) . Thus, the relative ability of different fish species to exploit high food abundances changes with temperature and size of the individuals . Such differences affect intra- and interspecific segregation along temperature gradients as well as seasonal consumption rates and size-dependent growth rates, processes that are important for interactions among fish species and between trophic levels (Magnuson et al . 1979 ; Brandt et al . 1980 ; Crowder and Magnuson 1982 ; Persson 1986 ; Rudstam et al . 1993). Maximum rations are also a component of many foraging models (Madenjian 1991 ; Brandt et al . 1992 ; Post and Rudstam 1992) and an integral part of bioenergetics models of fish growth . In addition, maximum rations are important to know for aquaculture . Bioenergetics models are balanced energy budgets evaluated throughout the life of the fish (Winberg 1956 ; Kitchell 1983). These models rely on
equations relating respiration and consumption to fish weight and temperature (Hewett and Johnson 1992). Often, these equations are derived from experiments covering limited size and temperature ranges, and they then have to be extrapolated to account for all fish weights and temperatures observed in the field, which can be problematic (Ney 1993). Post (1990) has shown that an extrapolation of an energetics model for "adult" yellow perch Perca flavescens (Kitchell et al . 1977) did not accurately describe the physiological rates of young-of-year yellow perch . We present results from experiments designed to evaluate the maximum consumption rates of bloater Coregonus hoyi over most of the range of fish size and temperature likely to be encountered in Lake Michigan (temperatures of 4-16ºC and fish weights of 1-200 g) . These data are used to derive an equation that predicts maximum consumption rates as a function of temperature and fish weight . In a companion paper (Rudstam et al . 1994, this issue), this equation is included as part of a bioenergetics model used to evaluate the production dynamics of bloater in Lake Michigan . Methods Lake Michigan bloaters were reared in the laboratory from eggs to the weights used in the experiments. The eggs were fertilized in the field
from spawning adults gillnetted in Lake Michigan during January-March 1979-1982 . The bloater eggs were incubated at 2-4ºC for approximately 60 d at the University of Wisconsin Great Lakes Research Facility . Thereafter hatching was stimulated by increasing the temperature in the hatchery jars to 6-7ºC, mimicking the conditions in Lake Michigan . Larvae were fed their first meals on brine shrimp nauplii Artemia sp . and fresh frozen zooplankton. As the fish increased in size, formulated flake and pelleted foods were also used . Adult frozen brine shrimp were incorporated into the diet to train the fish to the food to be used in the experimental trials . Maximum food consumption trials for bloaters nominally weighing 1, 5, 10, 25, 50, 100, and 200 g were conducted at 4, 8, 12, and 16ºC . The weight of bloaters actually used in each size group was within 10% of the nominal weight . Experiments were made with all combinations of temperature and fish weight except with 100-g fish at 12ºC ; the number of replicate trials for each combination ranged from two to eight . Over 125 trials were run with different combinations of bloater size and temperature . These trials were conducted in successive runs of about eight trial tanks per run from September 1979 through April 1983 . For each run, bloaters from holding tanks were anesthetized with MS-222 (tricaine) and sorted into four replicate tanks for each weight group . Wet weights of the individual fish were recorded to the nearest 0 .01 g . The 1- and 5-g fish were stocked into 0 .6-mdiameter circular tanks (110-L volume), the 10-, 25-, and 50-g fish were stocked into 189-L oval tanks, and the 100- and 200-g fish were stocked into 1 .22-m-diameter circular tanks (454-L volume) . At sizes of 50 g and smaller, six to eight fish were stocked in each trial tank ; at sizes of 100 and 200 g, three or two fish were stocked in each trial tank . Each tank was provided with a 4-L/min inflow of dechlorinated tap water derived from a Lake Michigan source . The standpipe plugs were fitted with 500-um nitex screening in order to retain uneaten food particles . The standpipes were further surrounded with 1-mm-mesh screening supported by 7 .6-cm-diameter plastic pipe in order to catch larger particles and prevent the smaller mesh from clogging . The temperature of the tank was controlled through blending of the hot and cold water supplies and adjusted from the holding tank temperature to the experimental temperatures at a rate of 1°C/d. This adjustment to experimental temperature was never more than a total of 5ºC, because the holding tank temper-
atures (9-12ºC) were close to the experimental temperatures . The fish were acclimated to the test tanks and test temperatures for 22-23 d . During acclimation, the fish were fed adult frozen brine shrimp . The ration was adjusted depending on fish size and the experimental temperature to a level representing ad libitum rations (3-30 g, determined by preliminary feeding trials) . Two to 3 d prior to the feeding trial, the number of fish was adjusted to exactly five for trials with fish of 50 g or smaller . The inclusion of extra fish during acclimation provided for possible mortality during the acclimation period, but mortality was low . There was never any need to add more fish to the experimental tanks . Three 100-g fish and two 200-g fish were used per trial tank . We had to use fewer large fish to ensure an adequate supply of large fish within narrow size ranges for all experimental treatments . Prior to the actual consumption trials, the fish were fasted for 47 h for the 12ºC and 16ºC trials and for 71 h for the 4ºC and 8ºC trials . During the acclimation and the 24-h feeding trials, temperatures were controlled to within 0 .5ºC of the intended experimental temperature . To ensure consistency of the adult frozen brine shrimp, excess water was drained from thawed 454-g packages of frozen brine shrimp first by straining the food through cotton cloth nets (for up to 4 h) and then by vacuum filtering (for up to 10 min) the water from the food with a buchner funnel until water stopped dripping from the funnel . These preparations were carried out under refrigeration . The food was then weighed and refrozen into blocks weighing approximately onesixth of the estimated daily ration . The relationship between wet and dry weight of Artemia was measured by drying several sizes of Artemia blocks at 60ºC (1-64-g blocks) . The water content ranged between 85 and 86% for all measurements (average, 85 .5%) . For each experimental run, the fish in each trial tank were fed to slight excess at 4-h intervals for 24 h . The feeding time for each of the tanks was staggered at 0 .5-h intervals to allow sufficient time for the postexperimental procedure . At the completion of a 24-h feeding period, any uneaten food on the bottom of the tank was collected by siphoning, then run through a combination of finemeshed aquarium nets and cotton cloth nets, which were then refrigerated for later weighing . Finemeshed aquarium nets were swept through the water column of the tank to collect any visible food material that remained suspended ; these nets
were also refrigerated for later weighing. The finemesh screening covering the standpipe was removed with attached uneaten material and refrigerated . These screens and nets containing the collected food material were carefully washed into a bucket . The material in the bucket was collected on cotton cloth and resuspended in as little water as possible (approximately 300 mL), and then filtered with the buchner filter until water stopped dripping . The remaining food was then weighed on the filter, and the filter weight was subtracted to determine the weight of uneaten food . Maximum daily ration for the group of fish was calculated by dividing the total amount of food consumed by the total weight of all fish in each trial tank . Following completion of a trial and removal of uneaten food, the fish were fasted for an additional 2 or 3 d to allow their guts to clear . Then they were killed with an overdose of MS-222 and their final wet weights were measured . Dry weight of the fish was determined following oven drying at 65ºC to a constant weight (
