Enclosures study of trophic level interactions in the mesotrophic part of Lake Balaton

Experiments with lake enclosures, open at top and bottom, were conducted to determine the effects of benthivorous fish, particularly bream (Ambramis brama), on the ecosystem. The fish-containing enclosure showed lower transparency throughout the study period. This markedly affected concentrations of suspended solids and chlorophyll-a. Nutrient increases in the fish-containing enclosure gave rise to corresponding increases in phytoplankton biomass and production. The introduction of fish to the enclosure led to the replacement of diatoms by mixed populations of filamentous cyanobacteria. Subsequently, at lower fish stocking levels, there was a shift in algal structure towards chlorophytes.