Alien Fish Species in Volga and Kama Rivers: Species Composition, Identification Peculiarities and Dispersal Patterns

Study presents information on alien fish species of the Volga and Kama rivers. The share of alien species in the total number of fish species in the catch in the Volga River basin varies from 8–10% (including large tributaries—the Sheksna and Oka rivers) to 36–47% (the Saratov and Kuibyshev reservoirs). For the Kama River reservoirs, the share of invasive species is lower—from 8% in the upper part of the river to 27% in the Votkinsk Reservoir. The observed highest proportion of alien species in the ichthyofauna of the Kuibyshev Reservoir is associated with its transit location along the northern (Caspian-Volga-Baltic) invasive corridor. The results of DNA analysis reflect the different directions of colonization of reservoirs of the Volga-Kama cascade by alien species. A significant portion of these invaders likely originated from the Azov-Black Sea basin. The complex history of differentiation and dispersal of many species creates difficulties in identifying taxa and genetic lineages of Azov-Black Sea and Caspian origin. This, in turn, complicates the monitoring of biological invasions. It is hypothesized that the expansion of Ponto-Caspian species’ ranges across the Volga basin was historically determined by a complex of adaptations developed by modern invasive species during the Paratethys period. To ensure rational nature management and control of biological invasions, long-term monitoring of fish communities in several “hot spots” in the Upper, Middle, and Lower Volga basins is essential. The most effective strategy for preventing biological invasions is maintaining high species richness and preventing overexploitation of fish stocks (especially piscivorous species). In this case, in less disturbed natural communities, native species act as a biological barrier (“living shield”), occupying accessible niches. Therefore, even if an invasive species enters, its naturalization is difficult. Currently, there is no need for priority conservation measures related to alien fish species in the Volga-Kama basin. From a rational nature management perspective, for the majority of already naturalized alien fish species, the optimal approach at this time is non-interference and the justified exploitation of this new resource.