Effect of Farming Fish Density on Zooplankton Community of Reservoirs

To assess the potential differences in predation impact on zooplankton by filter-feeding fish,zooplankton communities of three reservoirs with different fish densities and trophic levels in southern China were investigated.Zooplankton biomass was below 1.0 mg/L in the three reservoirs.Helong Reservior,which was eutrophic and cultured with highest density of filter-feeding fish,it's zooplankton biomass was significantly lower than that in the two other reservoirs.Baihualin Reservoir which was eutrophic with medium fish density,zooplankton biomass was much higher than Furongzhang Reservoir which was oligo-mesotrophic with low fish density.While zooplankton community was dominated by rotifera(Asplanchna priodonta) in Helong reservoir all year round.The zooplankton were dominated by cladorcera(Bosmina longirostris,Bosminopsis deitersi,Diaphanosoma dubium) in March and December,and by copepoda(Phyllodiaptomus tunguidus) in August in Furongzhang and Baihualin.Biomass ratios of zoo/phyto was always below 0.1 in the three reservoirs and had a significantly negative correlation with annual fish catch.Consequently,high predation by filter-feeding fish caused low biomass and dominance in small-sized zooplankton species in these reservoirs.