Prey selection by young yellow perch: The influence of capture success, visual acuity, and prey choice

Field and laboratory studies of prey selection by age-0 yellow perch Perca flavescens from Oneida Lake, New York, were conducted during 1980 and 1981. In paired analyses, laboratory fish proved to be good models of those in the lake; fish in both groups ate zooplankton of the same mean sizes and shifted their preference from Diaptomus minutus to Daphnia pulex when they reached 30-35 mm total length. Increased preference for daphnids over diaptomids coincided with the ability of young yellow perch to catch the daphnids with nearly 100% success. Neither laboratory nor field fish selected the largest daphnids available, though tests showed they were physically capable of ingesting them, and experimental data on capture success, handling time, and reaction distance all suggest young yellow perch should elect the largest daphnids. We hypothesize that young yellow perch may digest large daphnids less efficiently than midsized ones. If this hypothesis is verified, optimum-foraging models should be extended to incorporate food assimilation.