The article gives the analysis of infestation of Siberian sterlet Acipenser ruthenus marsiglii by parasites in the Lower Irtysh within 2017 to 2019. The annual changes in the species composition of parasites and in quantitative indicators of the fish infestation were revealed. In 2017 there were found 10 species of parasites, of which 4 were specific: Trypanoplasma acipenseris, Haemogregarina acipenseris, Acrolichanus auriculatum, Capillospirura ovotrichuria; in 2018 - 11 species, of which 6 were specific: T. acipenseris, H. acipenseris, Sphaerospora colomani, A. auriculatum, Truttaedacnitis clitellarius, Capillospirura itrichura; in 2019 - 7 species of parasites, of which 4 were specific: T. acipenseris, H. acipenseris, S. colomani, A. auriculatum. Of the broadly specific parasites, 6 species have been recorded: Trichodina acuta, Trichodina nigra, Trichodina sp., Diplostomum chromatophorum, Piscicola geometra, Unionidae gen. sp. In Siberian starlet blood there were registered T. acipenseris and H. acipenseris in all years of research. An increased extensiveness of invasion by these parasites was established. A significant decrease in infection with A. auriculatum trematode was found. The nematode C. ovotrichuria was recorded in sterlet only in 2017 and 2018. High values of infestation with Trichodina acuta, Trichodina nigra, Trichodina sp.were recorded. Myxosporidium Sphaerospora colomani was first recorded in the Ob-Irtysh basin. It has been suggested that the annual changes in the species composition of sterlet parasites are associated with the direct impact of the temperature regime and fluctuations in the level of the Irtysh basin
parasitofauna, Acipenser ruthenus marsiglii, sturgeon species, the Lower Irtysh, Trypanoplasma acipenseris, Haemogregarina acipenseris, Acrolichanus auriculatum, Capillospirura ovotrichuria
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