Structural and Functional Characteristics and Fatty Acids of Zoobenthos in a Section of the Ob River and in Its Tributaries

The species composition and fatty acid composition, seasonal dynamics of biomass, and production and productivity of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) of the zoobenthos of the Ob River and its tributaries, the Inya River and the Tula River, have been studied. The total contents of EPA and DHA in all taxa of zoobenthos are relatively high, except for Trichoptera, Bivalvia, and Gastropoda. Values of the EPA and DHA contents fall in the ranges reported in literature for the relevant taxa from various habitats, which confirms the hypothesis about the principal contribution of the phylogenetic factor to the contents of EPA and DHA of zoobenthos. The similarity of the species composition between the Inya River and the Tula River is lower than that between the Ob River and each tributary, which may be due to different hydrological features and types of bottom sediments, as well as a drift of benthic invertebrates from the tributaries into the main channel. The Ob River, the Inya River, and the Tula River have nearly similar values of zoobenthos production and EPA and DHA of productivity, while they differ from these parameters of the Yenisei River and its tributaries reported in literature, which have another species composition of benthic invertebrates. The EPA and DHA productivity, i.e., the biochemical quality of the fish food under similar values of the production of zoobenthos, is determined by the species composition of zoobenthos, which depends on the complex of environmental factors.