Invasion of Gymnocephalus cernuus (Linnaeus, 1758) by Alien Trematodes Apophallus muehlingi (Jagerskiold, 1899) and Nicolla skrjabini (Iwanitzky, 1928) in the Confluent of the Kuybyshev Reservoir

For the first time, information about the alien trematodes Apophallus muehlingi (Jagerskiold, 1899) and Nicolla skrjabini (Iwanitzky, 1928) found in Gymnocephalus cernuus (Linnaeus, 1758) in the Bolshoy Cheremshan River (Kuybyshev Reservoir) is presented. The timing of their penetration into the reservoir and the vector of invasion have been determined. In the studied section of the river, the formation of parasitic systems with the participation of alien parasites and G. cernuus is at the initial stage. Invasion of fish by trematodes associated with Lithoglyphus naticoides (Pfeiffer, 1828) indicates the introduction of this mollusk into the Bolshoy Cheremshan River. Differences in fish infection parameters from year to year were noted. A stable increase in the parasite prevalence of G. cernuus by A. muehlingi metacercariae and high values of this indicator for N. skrjabini for 3 years confirm the rapid rate of naturalization and number growth of L. naticoides in the reservoir. The possibility of rapid formation of an extensive hotbed of apophallesis in the lower reaches of the river is noted. The significant role of climatic and hydrobiological conditions in the realization of the life cycles of alien trematodes is shown. Currently, the combined influence of economic activities and environmental factors has facilitated the creation of favorable conditions for the penetration of alien species of aquatic organisms from the Kuybyshev Reservoir into the Bolshoy Cheremshan River. Further distribution of invader species in the reservoir ecosystem, inclusion in the trophic chains of river and near-water terrestrial ecosystems, and expansion of the host range of alien parasites are predicted.