Following the results of long-term investigation of the Chogray Reservoir, carried out in the period from 2010 to 2020, the data on its hydrological and hydrochemical regime and the current composition of its ichthyofauna are presented. The ichthyological material has been collected and processed according to generally accepted methods. The stocks and abundance have been calculated using the method of direct counting per area unit. The results of this investigation indicated that the formation

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... f the species composition of fish in the reservoir was influenced by biotic and abiotic factors and passed several stages. At the first stages of the formation of the ichthyofauna of the Chogray Reservoir, common carp, Prussian carp and zander prevailed in its species composition. The basis of the ichthyocenosis of the Chogray Reservoir was and proceeds to be composed of demersal species. In 1972, the acclimatization of common bream was carried out. In the first years of commercial exploitation of the reservoir, the main fishing target was carp, which by the early 1980s began to be replaced by common bream. The main commercial fish species in the Chogray Reservoir are the following, in order of their abundance: common bream, European perch, Prussian carp, common roach, common carp, and white bream. It is established that in the last years of operation of the reservoir, the fish community has undergone certain changes that are associated with hydrological and hydrochemical fluctuations. Currently, the biodiversity of the ichthyofauna is represented by 22 species and subspecies of fish. The percentage for species distribution of commercial fish species in the ichthyofauna of the Chogray Reservoir is presented (in 2020, the share of common bream was 56 %, and Prussian carp and European perch accounted for 14 % each). The reduction in the exploitable volume of water in the reservoir led to an increase in the area of shallow waters, their overgrowth, a reduction in the stocks of the main commercial fish species and an increase in the population of tench. The average water salinity increased from 1.9 to 2.7 g/L. During the commercial exploitation of the reservoir, significant fluctuations in catches were recorded.