Abstract
Fish occurring in the outlets of water basins reduce the abundance of zooplankton. The study was performed at the outlet sections of the lake and waste stabilization pond of a sewage treatment plant. The aim of the study was to determine which zooplankton is chosen more often by the roach (Rutilus rutilus), those drifting from the waste stabilization pond or from the lake. The zooplankton from the pond was dominated by Daphnia pulex while zooplankton from the lake was dominated by small planktonic rotifers. We observed that the larger the plankter-victim’s size, the faster the reduction of its number. The fish were more likely to feed on zooplankton drifting from the waste stabilization pond than from the lake. It was influenced by D. pulex individuals, attractive for fish due to their largest body size among the analyzed zooplankton. The significance of riverine zooplankton in the downstream food web may render this data even more important.
Highlights
Fish make the most significant contribution to reduction of zooplankton communities [1,2,3,4,5]
Certain authors speculate that fish are the main factor reducing zooplankton biomass in outlets [6,7,8], while others prove the point by showing zooplankton in fish stomach contents [9]
Phytoplankton communities and chlorophyll a concentration were not determined during the study, these findings could have been useful for determining feeding conditions for D. pulex
Summary
Fish make the most significant contribution to reduction of zooplankton communities [1,2,3,4,5]. This is especially visible in lake outlets where drifting zooplankton constitutes a rich food base for fish [6,7]. There is scarce literature regarding the efficacy and food selectivity of fish feeding in outlets of stagnant water basins. Certain authors speculate that fish are the main factor reducing zooplankton biomass in outlets [6,7,8], while others prove the point by showing zooplankton in fish stomach contents [9]. There is a lack of studies showing the stomach content of fish in regard to the zooplankton food-base in a river and the size of zooplankton victims
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