The influence of ecological features of the Novosibirsk reservoir on its infection with Metorchis bilis

Abstract

The West Siberian region is the focus of the spread of opisthorchiasis. The first intermediate hosts of these trematodes are pregill gastropods of the fam. Bithyniidae (Gray, 1857). Mollusks eat the eggs of these parasites, and after a cycle of asexual reproduction, opisthorchid larvae (cercariae) emerge from them, which swim in the water and penetrate into the bodies of fish through the skin. Danger for humans and carnivores is represented by fish of carp species (second intermediate hosts), but most often parasites of this fam. Opisthorchidae (Loose, 1899) occur in the ide (Leuciscus idus (Linnaeus, 1758)). The article presents data on the modern ichthyoparasitological state of the ide from the Novosibirsk reservoir and its abundance in the reservoir, on the places of mass accumulation of fish and mollusks in the reservoir, and describes the feeding habits of the studied fish. The relationship between the trophic preferences of this fish species and the indicators of its infection with opisthorchids is revealed: the ide, which feeds mainly on mollusks, lives in those parts of the reservoir where it can satisfy its needs, being in the zone of maximum risk of infection with trematode cercariae. The article explains the surge in infection of an ide from the reservoir with the trematode Methorchis bilis (Braun, 1890) in 2020. The hydrological regime of the reservoir, which is unfavorable for gastropod mollusks, and the presence of an alien species of gastropods Viviparus viviparus (Linnaeus, 1752) competing with bithyniids, as a rule, restrains the growth in abundance molluscs fam. Bithyniidae, which also affects the distribution of opisthorchiasis in fish, however, favorable conditions in 2020 allowed the population of mollusks to increase their numbers, which caused an increase in invasion rates in ide.