Effect of Competition Between Two Freshwater Fishes on Prey Consumption and Abundance

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Abstract
The effect of inter- and intraspecific competition on the type and quantity of food consumed by fish, and on the abundance of macroinvertebrate prey, was examined by manipulating densities of yellow perch (Perca flavescens) and pumpkinseed (Lepomis gibbosus) stocked into littoral zone enclosures at levels approximating 0.5, 1.0, and 2.0 times the measured total fish biomass on the littoral zone. In intraspecific competition experiments, neither species showed a change in the type of prey eaten (principally macroinvertebrates). The amount of food eaten by yellow perch reared at high (26 g/m2) densities was significantly depressed relative to that of perch reared at low (6.5 g/m2) and natural (13 g/m2) densities. There were no significant differences in the amount of food eaten by pumpkinseed at the three fish densities. The gut fullness of pumpkinseed reared at high densities, however, was biased to a significant but unknown degree by the inclusion of a nonfood item, macrophyte fragments, in the estimates. No other fish consumed macrophytes. In interspecific competition experiments, the gut fullness of yellow perch and pumpkinseed reared together (combined density 13 g/m2) did not differ from that of fish reared alone at low or natural densities. The diet (principally macroinvertebrates) of the superior competitor, pumpkinseed, did not change relative to that of pumpkinseed reared alone. The inferior competitor, yellow perch, exhibited a significant change in diet. Microcrustaceans (an energetically inferior food) comprised 30–53% of the diet (by weight) of yellow perch reared with pumpkinseed compared with < 1% of the diet of perch reared alone. Total macroinvertebrate biomass and abundance were unaffected by differences in fish biomass in the enclosures.