ИХТИОФАУНА МАЛЫХ РЕК СРЕДНЕГО ПОВОЛЖЬЯ (РЕКА КАЗАНКА)

Abstract

The article considers the specific structure of the fish fauna in the Kazanka River in the late XIX - early XXI. In the lower reaches of the river, according to the documents of 1995-1996, there lived 22 fish species, and in the middle part of the river there are16 species in 2009-2017. These are mainly representatives of the carp family (Cyprinidae), of which 9 species belong to the Ponto-Caspian faunistic complex and 10 species - to the boreal lowland. The amphiboreal complex consisted of 5 species. In the middle reaches of the river, unlike the lower reaches, a loach was encountered. Differences in species diversity in the lower and middle reaches of the river are associated with changes in the hydrological regime characteristic of the Kuibyshev Reservoir, which is observed in the river. The presence of a continuous current caused the disappearance or significant reduction in the number of commercial fish (pike perch, catfish, bluebone, sabrefish). In different years silver crucian, ruff and bleak dominated in fish catches in the middle reaches of the river, the abundance of which ranged from 27.5 to 86.4%. Starting from 2012 in the Kazanka River the proportion of crucian in catches increased significantly. This is connected with its transition from gynogenetic triploid form, when there were only females in the population, to diploid (bisexual) form, and with a high degree of resistance to various pollutants. In the catches there were found silver crucian species at the age 4+ - 8+ years, body length 12.0-22.0 cm. The growth of this species in the Kazanka river was slower than in the Volga reaches near Kuibyshev Reservoir. In some years, ruff also prevailed in the catches making up 27.5-47.7% of the total fish catch, but the fluctuation of its population was high due to the fish death caused by frequent discharge of polluted water into the river. In catches ruff occurred at the age of 0+ - 4+ , body length 5.0-12.0 cm. The body length of of even-aged ruff individuals in the river was less than that in Kuibyshev Reservoir. Bleak dominated in catches only in 2009, accounting for 86.4% of the catch. Shannon index on the Kazanka River in some years ranged from 0.94 to 2.57 bits and was defined by both the number of species and the indicator of abundance.