Results of the comprehensive fisheries survey of lake Biserovo in the summer of 2019

The article presents the results of field hydrological, hydrobiological and ichthyological studies on Lake Biserovo conducted in the summer of 2019. Analysis of water samples from Lake Biserovo showed that it is fresh, medium mineralized, medium hardness, bicarbonate class of the calcium group. In the conditions of summer stratification of water masses, low oxygen saturation of water at depths of more than three meters has been established throughout the profundal zone of the reservoir. Toxicological studies have shown a significant excess of the maximum permissible concentrations of cobalt, chromium and phenols in the water established for fishery reservoirs throughout the lake. According to the presence of algoflora indicator species, Lake Biserovo was classified as a mesosaprobic reservoir during the observation period. According to the species structure of planktonic communities and quantitative indicators of phyto- and zooplankton development in the summer of 2019, the lake corresponded to the trophic status of eutrophic reservoirs. Oxygen deficiency in the bottom horizons at depths of more than two meters, combined with the liquid consistency of sapropel silts, prevent the formation of stable benthic communities on a larger area of the bottom of Lake Biserovo. The current composition of the ichthyofauna of this reservoir is characterized by low species diversity and is characteristic of reservoirs exposed to long-term effects of organic pollution. The core of the ichthyocenosis is formed by eurybiont species that are resistant to living in reservoirs with unfavorable oxygen conditions. A characteristic feature of their populations in reservoirs of this type is the sharp predominance in catches of younger age groups due to high natural mortality in conditions of periodic summer and regular winter floods in the lake.