Possible way to restore the population of European grayling (Thymallus thymallus (Linnaeus, 1758)) in the small rivers on the example of the river Kosva

Morphological characteristics European grayling is investigated. An estimate is given of the content of 24 microelements in the tissues and organs of the European grayling and in the soil of the Kosva river (the basin of the Middle Kama river). It is established, that in 10-15 years after the cessation of the discharge of mine water in the Kosva river maximum content in organs and tissues of the European grayling described the reservoir is characteristic of manganese, zinc, strontium and barium, significantly lower concentrations of nickel, cobalt, chromium, copper, lead, silver and other elements, which is typical for graylings. The exception is the group of small grayling specimens of the river Kosva, for which noted high concentrations of a number of elements in the muscle tissue. Morphological characteristics of grayling in the submitted sample comply with the parameters of fishes between river and brook ecotypes. Probably, these results indicate the presence of European grayling from the lower part of the river Kosva migrations from places with a higher level of pollution (actually the river Kosva) to places with a low level of soil pollution (clean tributaries: Vilva, Pozhva, etc.) and back. Fish of older age groups such migration is likely to be larger than in fish of the younger age groups.