Fish effects on trophic relationships in the pelagic zone of lakes

To examine the relationships between the biomass of pelagic communities and to study how these relationships differ between lakes with different fish assemblages, we used data on nutrients, chlorophyll, zooplankton, and fish from 96 Argentinean lakes and reservoirs. Significant differences in regressions between chlorophyll and total phosphorus, macrozooplankton and chlorophyll, and between total fish and macrozooplankton, in lakes with different fish assemblages, were found. Lakes with zooplanktivorous fishes but without piscivores, and lakes without planktivores, had the highest and the lowest phytoplankton biomass, respectively. The regression line for lakes with both types of fish were intermediate. Furthermore, lakes with planktivores, but without piscivores, had the lowest macrozooplankton. The analysis of the trend in simple regression residuals suggests that the changes in chlorophyll, macrozooplankton, and total fish with lake trophy, are related to changes in fish assemblages.