Trophic differentiation of the nosed charr Salvelinus schmidti Viktorovsky, 1978 in Lake Kronotskoe (Kamchatka)

The nosed charr Salvelinus schmidti that inhabits the littoral zone of Lake Kronotskoe is divided into two groups according to food preferences and parasite fauna. Fish of the first group (G) predominantly feed on gammarids and are characterized by a high infestation with Cystidicola farionis, Cyathocephalus truncatus, and Crepidostomum spр. Fish of the second group (A) do not consume gammarids but feed mostly on chironomid larvae and pupae and on mollusks; the predominant parasites are Phyllodistomum umblae and Proteocephalus longicollis. The significant difference in the abundance of C. farionis, which remains in fish at least for 2 years, is indicative of a long-term and persistent trophic diversification between the charr groups. Moreover, significantly higher growth rates, a larger body size, and a longer lifespan are observed for fish of group G. The feeding strategy of the nosed charr is maintained throughout the life and does not depend on the sex of fish and their distribution within the littoral zone of the lake.