No General Percid Dominance under Mesotrophic Lake Conditions: A Test of Several Hypotheses

Several hypotheses concerning the dominance of percids under mesotrophic lake conditions were tested in five lakes of intermediate trophic state, situated in northeastern Germany. In contrast to prediction, the fish communities in four lakes were dominated by cyprinids (roach, Rutilus rutilus and bream, Abramis brama), while percids (Eurasian perch, Percafluviatilis) dominated in one lake only. Percid biomass was not positively related to macrophyte cover, and age-0 perch exhibited no switch from zooplankton to benthic prey during summer in all lakes studied. Perch of the size-class 100-150 mm were partly piscivorons in the lakes not dominated by perch, while they were more benthivorous in the other. Perch larger than 150 mm were piscivorous in all lakes, though those in the lake dominated by perch had to a large extent consumed benthic invertebrates in spring. Roach utilized macrophytes instead of bluegreen algae as an important food resource and otherwise were mainly benthivorous. Thus, important predictions concerning the structure of fish communities in mesotrophic Eurasian lakes could not be verified by this study.