THE EFFECT OF FISH ON PLANKTONIC ROTIFERS

The dynamics, community structure, and productivity of planktonic roti fers were studied during 3 years in two lakes near St. Petersburg (Rus sia). One lake was repeatedly stocked with larvae of the fish Coregonu s peled; the other contained no fish. Fish addition led to a shift in plankton community structure. Population densities of some rotifer spe cies (Keratella cochlearis, K. irregularis, Asplanchna priodonta) incr eased as a result of the elimination of large crustaceans by fishes du ring summer and autumn. An inverse relationship was found between the biomass of rotifers and Daphnia.