Features of Trematode Communities in the Ponto-Azov Snail Lithoglyphus naticoides (C. Pfeiffer, 1828) (Gastropoda, Hydrobiidae) from the Uglich and Rybinsk Reservoirs (Upper Volga Basin)

The freshwater gastropod mollusk Lithoglyphus naticoides (C. Pfeiffer, 1828) naturalized successfully in the Rybinsk Reservoir and in the Uglich Reservoir in 2005–2011 and 2013–2015, respectively. The aim of this work is to study the structure of trematode communities in settlements of L. naticoides formed by 2019 in the upper parts of these water bodies. It is found that, in both reservoirs, the species composition of trematodes is similar and includes Apophallus muehlingi (Jägerskiöld, 1899), Apophallus (=Rossicotrema) donicus (Skrjabin et Lindtrop, 1919), Parasymphylodora markewitschi Kulakowskaja, 1947, Nicolla skrjabini (Iwanitzky, 1928), and Sanguinicola volgensis (Razin, 1929). The density of L. naticoides varies from 30 to 50 ind./m² in the shallows of the Rybinsk Reservoir and from 50 to 520 ind./m² in the Uglich Reservoir, where the mollusk is found at the depth of 2–9 m. In August 2019, the prevalence of parthenitae varied at different degrees even in relatively flowing upper parts of the reservoirs similar in hydrological characteristics: Apophallus spp. (32.01 and 11.45%), P. markewitschi (9.14 and 7.63%), N. skrjabini (16.57 and 7.63%), S. volgensis (19.43 and 63.36%). In the Uglich Reservoir, Xiphidiocercaria sp. (9.16%) has been recorded, though their species has not yet been determined. A single case of mixed infection with parthenitae of trematodes (Sanguinicola + Nicolla) was recorded in the Rybinsk Reservoir in 2019. In the Uglich Reservoir, mixed infection with two species of parasites is more common (Parasymphylodora + Xiphidiocercaria, Sanguinicola + Xiphidiocercaria, Sanguinicola + Parasymphylodora, Sanguinicola + Nicolla). Owing to the high occurrence of some trematodes, L. naticoides is able to have a significant impact on the ecosystems of reservoirs by the development of foci of the helminthoses even with a relatively low size of its populations.