PHYTOPLANKTON OF IRRIGATION RESERVOIRS UTILIZED FOR FISH FARMING

In 1987-1989 the species composition of phytoplankton, its abundance a nd chlorophyll concentrations were studied in the irrigation reservoir s Petrova Ves and Prietrz (West Slovakia). Resevoirs were utilized not only for irrigation but also for production of stocking and marketabl e carps as well as in two-year cycles. The phytoplankton community of both reservoirs is very similar in species composition and development dynamics and is considered to be a typical pond community. A total of 270 algal taxa were identified, of which 14 were observed in Slovakia for the first time. In Petrova Ves we recorded 221 taxa and in Prietr z 178. Chlorophytes and diatoms represented the largest proportion in both reservoirs. The chlorophyll a content reached maximum concentrati on during spring and autumn. Generally higher values of chlorophyll as well as in the mean summer concentration of chlorophyll were measured in Petrova Ves, where remarkable differences were monitored during gr owth season. The abundance of phytoplankton and content of chlorophyll in both reservoirs of the study were lower in years of fish stocking than in the year of harvesting marketable fish. The phytoplankton comm unity of Prietrz was more stable, cell concentrations and chlorophyll content were lower here, without any remarkable differences during the year of study.