Two different feeding tactics of young-of-the-year perch, Perca fluviatilis L., inhabiting the littoral zone of the lowland Sulejow Reservoir (Central Poland)

The feeding pattern of young-of-the-year (YOY) fish was investigated in a field experiment in the sparsely vegetated littoral zone of the Sulejow Reservoir in June 2007. Perch received special emphasis in this study. During the study period, the part of the reservoir selected to conduct the research was densely inhabited by YOY fish (up to 20 individuals per square metre). The dominant YOY species were perch (Perca fluviatilis) and roach (Rutilus rutilus). Analyses of stomach/gut contents showed that large zooplankters and benthic prey contributed significantly to the diet of YOY fish. For perch, two distinct feeding tactics were observed. Fish collected by trapping in unvegetated gaps among beds of macrophytes preyed almost exclusively on daphnids and copepods, whereas individuals seined in shallow water among macrophytes ate mostly the larvae of benthic insects. The observed division of YOY perch into two feeding groups may indicate an attempt to decrease the level of both intra-specific competition among the cohort's members and inter-specific competition between perch and roach.