SELECTED MORPHOMETRIC CHARACTERISTICS OF MASS SPECIES OF FISH POPULATION IN THE LOWER IRTYSH
To study the fish population of the Lower Irtysh there were used control catches in the lower Irtysh in the Uvatsky, Tobolsky and Vagaysky regions of the Tyumen oblast. The results of forensic ichthyologic examinations on such species as nelma, starlet and Sibirian sturgeon, were used by the members of Aquatic ecology group of the Tobolsk Complex Scientific Station of the Ural Branch of the RAS. There were investigated representatives of six families (Cyprinidae, Acipenseridae, Esocidae, Percidae, Lotidae, and Coregonidae), in total, 13 species of fish were studied with a total of 969 individuals. The most numerous were peaceful fishes - 825 individuals (representatives of the Cyprinidae family 73.0% and the Acipenseridae family - 12.2% of the total number of fish in the control catch). The proportion of predatory fish species accounted for 144 individuals (representatives of Coregonidae family - 0.2%, Percidae - 8.2%, Esocidae - 5.0% and the only representative of the Lotidae family - burbot, was 1.4% of the total catch). Maximum weight was noted in Siberian sturgeon - 7 880 g, the minimum mass recorded in roach was 41 g. Maximum fishing length among the fish studied was also noted in Siberian sturgeon - 105 cm, the minimum length noted was of dace - 8.9 cm. Presence in catches of such species as pike perch, ruff and burbot, which are sensitive to water pollution, can be considered an indicator of satisfactory water condition in the Lower Irtysh.