Impact of cyprinids on zooplankton and algae in ten drainable ponds

The role of cyprinids (bream, carp and roach) in determining algal and zooplankton biomass and physical and chemical water quality was examined in 10 drainable ponds, each divided into compartments with fish and without fish. Differences between the compartments included a higher density of Daphnia species in non-fish compartments (10-30 individuals of Daphnia hyalina per litre, compared with 1 individual in fish compartments), a higher density of cyclopoid copepods and Bosmina longirostris in fish compartments, and significantly higher turbidity in fish compartments, probably due to sediment resuspension by carp. There was no marked difference in nutrient concentration between fish and non-fish compartments.