Fish as a Factor Controlling Water Quality in Ponds

Plankton of the fish pond Velký Palenec reveals a two-year periodicity, which is induced by the two year cycle of fishery management. During the two years of each cycle the biomass of carp increases considerably, while their numbers decrease. Whitefish are grown with the carp. In the first year of each cycle transparency and light penetration are high, chlorophyll and primary production of phytoplankton are low, large Daphnia are abundant and small zooplankton is scarce. In the second year of each cycle the reverse is true. Implications for regulation of water quality in shallow eutrophic bodies of water are discussed.