Zoobenthos of the lower Ob and its importance in fish nutrition
The article presents the results of long-term studies of macrozoobenthos in the Lower Ob in the areas of Salemal and Yambura settlements during the anadromous migration offish from the Gulf of Ob. The analysis of the state of bottom-feeding fish food reserve for the six-year period up to 2001 and for the period from 2007 to 2020 was conducted. It was found that there were no significant changes in the qualitative and quantitative development of zoobenthos. There was no decrease in species diversity, the initial taxonomic composition of macrozoobenthos remained for 20 years of observations. The density of benthic invertebrates and their biomass are within the seasonal and multiyear values, the structure of benthic communities remains unchanged. The contents of 137 gastrointestinal tracts of three whitefish species were analyzed to assess the significance of zoobenthos in the diet of valuable commercial fish. It was found that the nutritional spectrum of muksun, broad whitefish, and Siberian whitefish includes about 30 food items, and more than half of them are common to all three species. Fish feeding was dominated by benthic invertebrates dominating in the macrozoobenthos of the studied section of the Ob River by number and/or biomass. These are larvae of amphibiotic insects and bivalves. In addition, muksun consumed zooplankton and nectobenthos, broad whitefish and Siberian whitefish consumed isopods. The maximum indices of stomach-filling were observed in fish whose food bolus was dominated by isopods or bivalves. The food reserve of the Lower Ob in the study area provides the nutritional needs of bottom-feeding fish, feeding conditions of muksun, broad whitefish, and Siberian whitefish are favorable.