THE EFFECT OF DIFFERENT FISH COMMUNITIES ON THE CLADOCERAN PLANKTON ASSEMBLAGES OF THE KIS-BALATON RESERVOIR, HUNGARY

In 1995 the authors studied the effect of different fish communities o n the structure of the cladoceran plankton in a shallow hypertrophic l ake. After a fish kill of 1991, different fish communities developed i n the Kazetta and the outer area of the Kis-Balaton reservoir. In the outer area of the reservoir, the densities of plankton feeding fish sp ecies were considerably higher than in the Kazetta. These differences induced changes in the structure and dynamics of the cladoceran plankt on. The biomass of small-bodied cladocerans (mainly Bosmina longispina ) was higher and the biomass of the large-bodied cladocerans (D. hyali na, D. magna) was lower in the western and eastern part of Kis-Balaton reservoir than in the Kazetta. A peak in cladoceran biomass in the Ki s-Balaton reservoir was observed during the summer, close or during a bloom of filamentous cyanobacteria, whereas in the Kazetta a peak was observed during the spring, before the bloom of cyanobacteria. The adu lt females of D. hyalina were larger and produced more eggs in the Kaz etta than in the outer area of the reservoir.