Parasites in rotifers from the Volga delta

Internal parasites were recorded in more than 20 species of rotifers from w ater bodies of the Volga delta. The most abundant species, Asplanchna priod onta Gosse and Brachionus calyciflorus Pallas, were infested every year. Th e infestation was usually recorded in May and June during the spring-summer maximum in abundance. B. calyciflorus was usually infested by Microsporidi um asperospora (Fritsch, 1895), while A. priodonta was more often infested by Pythium sp. and bacteria. At times, the incidence of infestation was as high as 20-40%. The main developmental stages of some parasites were examin ed and photographed on living material.