INFECTIOUSNESS OF BREAM ABRAMIS BRAMA BY MONOGENEANS (MONOGENEA) IN THE LOWER IRTYSH BASIN

In the Lower Irtysh basin there is rich diversity of the fish population, bream Abramis brama (Linnaeus, 1758) is one of the representatives. Having been introduced into the Ob’-Irtysh basin more than 100 years ago, it dispersed in most reservoirs due to its wide adaptive variability and high fecundity. In the process of fish introduction, the new types of parasites replenish the parasitic communities of water bodies. As a result of studying bream parasitic fauna after its distribution there has been stated a decrease in parasite species composition, in comparison with its maternal habitat. Studies conducted in 2017-2018 allowed to fund out infectiousness of bream with four types of monogeneans: Gyrodactylus elegans , Dactylogyrus falcatus , D. wunderi , D. zandti . There has been recorded 100% extensiveness of invasion by dactylogyruses. Extensiveness of invasion by G.elegans in 2017 amounted to 100%, in 2018 - 74.2%. The abundance index of G.elegans in 2018 decreased in comparison with 2017 and amounted to 55.9 and 83.4 specimens, respectively. Abundance index of Dactylogyrus spp. decreased in 2018 and amounted to 27.9 specimens, compared to 2017 when there were registered 55.9 specimens. In 2017, the examined bream individuals showed a total predominance of gyrodactyluses over dactylogyruses, whereas in 2018 the number of Dactylogyrus spp was higher than of G. elegans . The of infectiousness of bream was first established after its distribution in the Ob’-Irtysh basin, when it was infected by the specific monogenean - Dactylogyrus falcatus (Wedl, 1857).