Lake Maloe Yanisyarvi (Southern Karelia) hydrobiocenoses under commercial trout cultivation conditions

Based on our own and literature data, the state of the ecosystem of Lake Maloe Yanisjarvi (South Karelia) in the conditions of industrial trout farming (since 2020) has been analyzed. The reservoir belongs to the mineralized (24.4-31.6 mg/l), calcium sulfate class. The chemical composition of the waters is not subject to significant fluctuations throughout the year. Among the forms of mineral nitrogen, nitrate and ammonium predominate (the maximum concentration noted is 0.12 mg/l). The total phosphorus content does not exceed 0.012 mg/l, mineral – 0.01 mg/l. Fluctuations in the concentration of dissolved oxygen are in the range of 7.0-9.1 mg/l. High flow rate (indicator of conditional water exchange 3.5 year-1) is the main stabilizing factor contributing to the preservation of the hydrochemical regime of the reservoir. In general, the water masses of Lake Maloe Yanisjarvi in their chemical composition meet the requirements for the aquatic environment in the cage cultivation of salmon. The data on the main hydrological and hydrobiological indicators of the lake are presented. According to the level of quantitative development of zooplankton in the summer-autumn period, the lake corresponds to the oligotrophic type with a biomass of up to 1 g/m3, benthos – to the α-mesotrophic type (2.8 g/m2). The reservoir belongs to the highest fishery category, according to literature data, valuable fish species (salmon, trout, whitefish and grouse) are noted as part of the ichthyofauna. Recommendations on the timing of the ecological expertise of the lake are given.