Assessment of the Impact of the Invasive Mollusk Viviparus viviparus (Linnaeus, 1758) (Mollusca, Gastropoda) on the Biochemical Quality of Fish Food Resources in the Lower Reach of the Ob River Reservoir

The impact of the invasion of Viviparus viviparus (Linnaeus, 1758) into the lower reach of the Ob River Reservoir on the biochemical quality of the fish food resources was assessed. In the invasion of V. viviparus, a decrease in the weighted average content of essential polyunsaturated fatty acids—eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)—was observed in the biomass of zoobenthos. However, the biomass, production, and productivity of EPA and DHA in native zoobenthos remained unchanged, as the invasive mollusk occupied a vacant trophic niche. In the river area under study, benthivorous fish after the invasion of V. viviparus can potentially receive the same amount of polyunsaturated fatty acids—essential for their growth and development—from zoobenthos production as before.