Ecology, biology and nutrition of grayling (Thymallus thymallus Linnaeus, 1758) of river Sotka in Pinezhsky State Reserve

European grayling Thymallus thymallus (Linnaeus, 1758) is the most valuable nonmigratory species in the ichthyofauna of the Pinezhsky Reserve. The grayling’s habitat inside the specially protected natural area is the Sotka river - the main attraction in the Reserve - flowing through its karst gorges. There are presented the results of comprehensive ichthyological study of grayling population in the Sotka river. Data on the ecology, biology, linearly-weight characteristics and age structure of the population are given. It was found out that grayling prefers the water areas with a mountainous (fast) flow, where it dominates among the fish species and forms a core of the local ichthyocenosis. Specific features of nutrition and age-related changes in the grayling diet have been studied. The 18 taxonomic groups of invertebrates, vertebrates and aquatic vegetation were registered in the food spectrum. The nutrition grayling base in the summer was presented by benthic larvae of amphibiotic insects, planktonic and nektonic organisms. The older species had a narrower range of nutrition based on ground-air insects, while the juveniles' diet was dominated by aquatic insect larvae. By the nature of nutrition, graylings in the river Sotka are euryphages, whose basic diet consists of arthropods. The multi-age structure and abundant population indicates prosperous state of these species.