Activities of radionuclides were measured in five species of fish (grayling, dace, crucian carp, pike, cod) sampled in the Yenisei River (Siberia, Russia) in the vicinity of the Mining-and-Chemical Combine (ROSATOM) from 2007 to 2010, with a gamma-spectrometer (Canberra, USA). The analyses of samples of organs and tissues of fish species revealed artificial (46Sc, 51Cr, 54Mn, 58,60Co, 59Fe, 65Zn, 85Sr, 99Mo, 103,106Ru, 137Cs, 141,144Ce) and natural (7Be, 40K) radionuclides in fish organs and tissues, including edible ones. The major percent (up to 80%) of 137Cs and 40K activity occurred in muscles of fish species, which also contained considerable percentages of 60Co (up to 70%) and 65Zn (up to 20%). Seasonal changes in the intake of artificial radionuclides by zoobenthos-feeding fish species (grayling and dace) were recorded and they were followed by an activity concentration increase in internal organs. The dramatic increase in radionuclide intake by grayling coincided with the change of diet source. Hence, the feeding behavior of fish can change the fluxes of artificial radionuclides in the Yenisei River. The most effective diet transfer of a radionuclide from gammarus to grayling (muscles and total body) was recorded for 40K (1.3) and much less effective for artificial nuclides.