[NUMBER DISTRIBUTION AND POPULATION STRUCTURE OF PROTEOCEPHALUS LONGICOLLIS (ZEDER, 1800) (CESTODA: PROTEOCEPHALIDEA), A PARASITE OF SMELT AND COREGONIDS].

The spatial structure and seasonal aspects in the number distribution of the cestode Proteocephalus longicollis population, maintained by trophic connections of specialized plankton-feeders (the vendace Coregonus albula L. and the smelt Osmerus eperlanus L.) in the Lake Onego were studied. Differences in the distribution of number of cestode population in host population, size-age structure, and pre-reproductive/reproductive stages ratio of the studied parasites were revealed. It was demonstrated that the spatial structure of P. longicollis was shaped by the specific characteristics of vendace and smelt populations in the Lake Onego. These species possess partially overlapping ecological niches and differences in the use of food resources, significantly determining the infection dynamics of the examined fish species.

[PARASITES OF THE COMMON ROACH (RUTILUS RUTILUS L.) UNDER THE IMPACT OF INDUSTRIAL POLLUTION OF A LAKE].

The consequences of man-induced transformation of Lake Kostomukshskoe (tailings dump) related to increased mineralization and entry of highly dispersed dredge material not typical for northern lakes were studied using roach parasites as the example. It was found that the roach parasite fauna has been losing rare and scant parasite species of different taxonomic groups, mainly helminthes with an indirect life cycle. Common and dominant species of myxosporidians, monogeneans, trematodes of genera Diplostomum and Tylodelphys have been preserved. The chances of survival are higher for those parasites with direct life cycle. Also the parasite species whose larvae can actively penetrate the host have been survived. The species Ligula intestinalis, Philometra rishta, Pseudocapillaria tomentosa had reported very rare. Fish are infected with these parasites by feeding of Copepoda and oligochaetes.