Biological and morphological characteristic of the Arctic grayling Thymallus arcticus (Thymallidae) from Alpine Lakes of the basin of the upper reaches of the Angara River

Specific morphological and biological features of the populations of the Arctic grayling Thymallus arcticus from lakes Urunge Nur, Mongosha, Sadaiskoe, and Gusinoe situated in the Upper Sayan Mountains in the sources of the Oka and Kitoi rivers (the basin of the upper reaches of Angara) that have been not studied previously are considered. The results of the multivariate analysis indicated the uniformity of all samples by 12 meristic characters. Graylings of the studied lakes are similar to graylings from the Angara and Nizhnyaya Tunguska rivers and the Irkutsk Reservoir, as well as to the Baikal grayling T. a. baicalensis in body coloration and pattern of the dorsal fin. The samples studied and T. a. baicalensis considerably differ in the above characters from populations inhabiting the basin of the upper reaches of the Ob that belong to the nominative subspecies T. a. arcticus. The differences established between the Angara-Yenisei and the Upper Ob graylings give grounds to doubt the justification of including them into one taxon, T. a. arcticus. The same is evidenced by the results of molecular-genetic studies of graylings from the Palearctic (Froufe et al., 2005). The data obtained indicate the necessity of ascertaining the boundaries of the ranges of different forms of graylings in the Angara-Yenisei and Ob basins and of the revision of their taxonomic status. Populations inhabiting the Angara and Yenisei rivers, except their sources and the section of the lower reaches, should be assigned to the Baikal subspecies, T. a. baicalensis. Graylings from different lakes in the upper reaches of Oka and Kitoi differ in their linear-weight indices. The indices of growth are highest where they occupy a dominant position. Their food in the summer consists mainly of the larval and imaginal stages of amphibiotic and aerial-terrestrial insects. Only in Lake Urunge Nur do graylings of elder age groups use fish of other species for food. The extreme conditions of habitation of the grayling in Lake Gol’tsovoe are the cause of food deficiency, which determines its dwarfism.