First year growth of European perch in reservoirs with different biotic and abiotic conditions

In central European meso- to eutrophic water bodies young-of-the-year European perch (Perca fluviatilis) belong to the most common fish species. On the other hand, water bodies with fish communities dominated by adult perch are disappearing rapidly and becoming extremely scarce. As a factor standing behind these declines in perch dominated fish communities, eutrophication and consequent better competitive abilities of juvenile roach for crustaceoplankton, the nearly exclusive food base in eutrophicated waters, have been suggested. Therefore, we have compared the growth rate of young-of-the-year perch in water bodies with abundant and non-abundant adult perch populations and related the observed differences to differences in the biotic and abiotic conditions of these water bodies, especially to differences in the food base and factors that affect these food base differences (macrophyte cover, oxygen vertical profiles etc.). Importance of the switch to piscivory in young-of-the-year perch and hence increased survival and dominance in the fish community is discussed.