Metozoic parasites of the Siberian sterland Acipenser ruthenus marsiglii (Brandt, 1833) Lower Irtish

The analysis of infection by metozoic parasites of the Siberian sterlet Acipenser ruthenus marsiglii of the Lower Irtysh depending on gender and age was carried out. Invasion by 9 species of parasitic organisms of 7 systematic groups was established (Cestoda - 1, Trematoda - 2, Nematoda - 2, Palaeacanthocephala - 1, Hirudinea - 1, Copepoda - 1, Bivalvia - 1). Of these, 3 species are specific parasites for sturgeons: Crepidostomum auriculatum (Wedl, 1858), Capillospirura ovotrichuria (Skrjabin, 1924) and Truttaedacnitis clitellarius (Ward & Magath, 1917). Widespread parasites of fish of the cestode Proteocephalus sp., comb Echinorhynchus cinctulus (Porta, 1905), crustaceans Ergasilus sieboldi (Nordmann, 1832), glochidia Unionidae gen. sp are noted singly at sterlet in LOWER IRTISH. Background mass parasites of the Siberian sterlet are the trematode C. auriculatum and the nematode C. ovotrichuria, which are parasitic in the gastrointestinal tract. With an increase in sterlet age, an increase in the invasiveness and abundance index of C. auriculatum is observed. Significant differences in the level of C. auriculatum infection between groups 2+ - 3+ and 6+ - 7+ (Phi-square = 0.17507), group 4+ - 5+ and 6+ - 7+ (Phi-square = 0, 11163). Nematode C. ovotrichuria parasitized in all age groups except the 6+ - 7+ group. With increasing age, an increase in the intensity of invasion by this parasite is noted. The rare specific parasites of the sterlet in the Lower Irtysh include the nematode T. clitellarius. This species was found in the intestine in three female sterlet, one specimen in each in 2 younger age groups. Diplostomum chromatophorum (Brown, 1931) and Piscicola geometra (Linnaeus. 1761) were found in all age groups with low rates of invasion. The dominant parasite at the age of 0+ - 5+ is C. ovotrichura, while C. auriculatum dominates in the 6+ - 7+ group. In males and females, parasite species are equally represented by single individuals. So, in males Proteocephalus sp. and Ergasilus sieboldi, in females - Echinorhynchus cinctulus and Unionidae gen. sp. Significant differences in the level of infection of C. auriculatum between groups of males and females were revealed. Male sterlets are more infected with C. auriculatum than females. In total, 7 species of parasites were found in females, and 6 in males. C. ovotrichura is the dominant parasitic species in both males and females. Thus, as a result of the study, an increase in the intensity and intensity of invasion by the background metozoic parasites C. auriculatum and C. ovotrichura with the age of the sterlet, as well as differences in the invasion of C. auriculatum in males and females, was established. T. clitellarius is a rare parasite of the sterlet in the Lower Irtysh.