Long-term Dynamics of Pike Infection by Parasites Triaenophorus crassus and T. nodulosus (Plathelminthes, Cestoda) in the Rybinsk Reservoir: Effect of Hydraulic Construction and Climate Warming

— The long-term dynamics (over more than 70 years) of pike infection by cestodes Triaenophorus crassus and T. nodulosus in the Rybinsk Reservoir (the Volga River) has been studied in a comparative aspect. Cestode T. crassus is an invasive species that has entered the reservoir together with vendace Coregonus albula (the second intermediate host) from Lake Beloe; T. nodulosus is a native species that develops with the involvement of perch as a second intermediate host. Climate warming in the Rybinsk Reservoir manifests itself in a consistently growing average water temperature. This has led to a gradual decrease in the rate of pike infection by cestode T. crassus as a result of disturbances in the set of complex ecological relationships between the parasite and its hosts: a decrease in the abundance of large pike, fluctuations in the reservoir water level, and mass death of vendace in years with abnormally hot summers and the alternation of strong and weak year-classes in this short-cycle species (age 1+ to 3+). The long-term dynamics of pike infection by T. nodulosus is characterized by its consistently high rates and slight fluctuations. The abundance of perch population in the Rybinsk Reservoir remains high, and its age composition is stable, which contributes to a high rate of infection of both perch and pike by T. nodulosus . Cestode T. crassus occurs only in large pike (30 cm long or more); the rate of infection increases with age; T. nodulosus parasitizes mainly young pike (starting from young of the year), with the infection rate decreasing in large pike.