ECOLOGICAL ASPECTS OF CHANGES IN THE FAUNA OF MULTICELLULAR PARASITES PERCA FLUVIATILIS LINNAEUS, 1758 (PERCIFORMES) IN THE TRIBUTARY OF THE KUIBYSHEV RESERVOIR

Abstract

The results of studies of the fauna of multicellular parasites of the river bass Perca fluviatilis Linnaeus, 1758, conducted in 2019-2021 in the Bolshoy Cheremshan river, a tributary of the Kuibyshev reservoir, are presented. Eight species of parasitic organisms and two representative genera related to Monogenea and Bivalvia were identified. A simplification of fauna structure of P. fluviatilis parasites that was noted could occur due to the loss of certain species, the invasion of which is associated with fish feeding with macrozoobenthos organisms. The study of species and quantitative composition of zooplankton community made it possible to establish the presence of possible intermediate hosts of parasites in the reservoir, the invasion by which is realized via trophic means. Parasitological data indirectly indicate a significant role of certain species of planktonic crustaceans in the nutrition spectrum of P. fluviatilis. In particular, the diversity of Crustacea (Cladocera, Copepoda) and close trophic connections of the fish with zooplankton community determine the degree of invasion of P. fluviatilis by some intestinal worms. The unstable dynamics of fish infection with the nematode Camallanus lacustris (Zoega, 1776) in the last two years associated with a high number of planktonic crustaceans Mesocyclops leuckarti (Claus, 1857) may indicate unfavorable conditions for the spread of the nematode in the reservoir. Information is provided on an alien species in the zooplankton community, i.e. Acanthocyclops americanus Marsh, 1893, and an impact of the crustacean on the native fauna of zooplankton is noted. Significant changes in the qualitative and quantitative characteristics of fish infestation that occurred over a relatively short time reflect the high rate of transformation of the fauna of P. fluviatilis macroparasites. In particular, since 2019, an alien species, Apophallus muehlingi (Jagerskiold, 1899), has been registered for the first time as part of the perch parasites of the studied reservoir. The interannual differences in the indicators of host infection show that the parasitic subsystem «A. muehlingi – P. fluviatilis» is at the stage of formation, the timing of the beginning of its formation has been determined.The vector of the spread of the alien parasite has been established – settlement with the first intermediate host. The trematode A. muehlingi has taken a dominant position in the fauna of the macroparasites P. fluviatilis. The rapid growth of the indicators of fish invasion A. muehlingi testifies to the high rate of propagation of the obligate first intermediate host of the parasite, the alien mollusk Lythoglyphus naticoides (Preiffer, 1828) in the studied area of the reservoir, and the close biotopic relationships of P. fluviatilis with the macrozoobenthos community. The relevance of the data obtained on the spread of trematodes in the Cheremshan river is determined by the sanitary and epizootological significance of A. muehlingi due to the pathogenicity of the parasite for the second intermediate (fish) and final (fish-eating birds, mammals/humans) the owners. The indirect influence of climatic (water temperature) and hydrobiological (level regime) factors on the success of the life cycle of A. muehlingi is analyzed. The results of the study showed that favorable conditions have now developed for the penetration of alien species of hydrobionts (macrozoobenthos, zooplankton, parasites) from the Kuibyshev reservoir into the ecosystem of the B. Cheremshan river.