The dynamics of radionuclide accumulation by fishes in different aquatic ecosystems was studied following the Chernobyl accident. Predatory and non predatory fishes in the Chernobyl NPP cooling pond, Kiev reservoir (Ukraine), Kojanovskoye lake (Russia) and Svyatoe lake (Belarus) were studied during the period 1986–1997. Concentration of radionuclides in fishes muscles decreased significantly during the period 1986–1997. Speed of purification of fishes depends on amount of radionuclides transferred in ponds and on hydrological and hydrochemical features of the aquatic ecosystems.