GAPE LIMITATION AND PREY SELECTION IN LARVAL YELLOW PERCH (PERCA-FLAVESCENS), FRESH-WATER DRUM (APLODINOTUS-GRUNNIENS), AND BLACK CRAPPIE (POMOXIS-NIGROMACULATUS)

We compared prey selection of larval yellow perch (Perca flavescens), freshwater drum (Aplodinotus grunniens), and black crappie (Pomoxis nigromaculatus) in Lake Mendota, Wisconsin. All three species had a diet dominated by copepods and selected progressively larger prey as fish length increased. For a given fish length, freshwater drum selected larger prey and black crappie selected smaller prey than yellow perch. These differences in prey selectivity were partly explainable from differences in gape to length relationships. Freshwater drum did have the largest gape for a given length of the three species, but gape size for black crappie and yellow perch were similar. Gape size predicted 67% of the variability in mean prey size ingested by yellow perch but only 15% for freshwater drum and 8% for black crappie. Although gape size did predict the upper limit of ingestible prey sizes and explained some of the differences in prey selectivity among the three species, both the degree to which the different fishes can ingest prey close to their gape limit and the degree to which gape predicted mean size of ingested prey varied among the three fish species.