[The etiology and diagnosis of "black spot disease" of fish].

Some traditional points of view on the black spot disease in fishes caused by the metacercariae of the trematode Posthodiplostomum cuticola are revised. The black spot disease should be considered as one of several symptoms appeared in freshwater and sea fishes in cases of infection with certain parasite species. Up to present days, more than 30 parasite species causing similar symptoms are recognized. And among them 8 such species have been recorded in fishes of the Volga-Caspian region.