Ichthyological aspects of implementing biological amelioration of the cooling pond of the Khmelnytskyi NPP

Purpose: The purpose of the work is to determine and analyze the main parameters, which characterize the impact of fisheries activities on the conditions for biological amelioration of the cooling pond of the Khmelnytskyi NPP. Methodology. Ichthyological material was selected from commercial catches of gillnets with a mesh size of 36-120 mm in the summer-autumn period of 2021 and the autumn period of 2024. A total of 244 net-days were analyzed, of which 2268 individuals of different species were collected for mass measurements, and 434 individuals for full biological analysis. The collection and analysis of materials were carried out according to generally accepted methods. To assess the theoretical survival of silver and bighead carps, the annual natural mortality rate was used, which was determined based on the natural mortality rate calculated using the parameters of the Bertalanffy equation. The abundance of silver and bighead carp generations for a given year was determined based on the volume of stocking, average natural mortality rates, and commercial catch parameters. The volume of stocking and catch was taken from official reporting data. Calculations were performed in MS Excel 2016. Findings. The majority of the commercial stock of the ichthyofauna of the studied pond in recent years were silver and bighead carps (on average 32.7%), Prussian carp (18.7%), roach (15.1%) and common carp (10.8%), the composition of dominant species was characterized by stability, with the exception of an increase in the share of Prussian carp. The actual stocking rates of the pond generally corresponded to the planned ones, however, the commercial catches amounted to only 12% of the planned ones. The average total mortality for middle age groups, according to the analysis of the catch curve, was φZ=0.42, which allows assessing their estimated annual catch at the level of φF=0.03…0.07. In contrast, for older age groups, the total annual mortality rate was φZ=0.47, while the average estimated annual fishing mortality was φF=0.26…0.27. Meanwhile, calculations of annual natural mortality for older age groups based on the analysis of the catch structure and catch statistics data gave the value φF=0.01…0.05. To localize the negative impact of secondary (due to increased natural mortality) pollution of the pond at an acceptable level, it is necessary to introduce moderate harvest of ichthyomas of middle age groups of biological control agents with an annual fishing mortality coefficient at the level of φF =0.05-0.10, and increased catch of age groups from age-7 and older with φF=0.30…0.40. To ensure maximum effect of biological control, the optimal gears for catching silver and bighead carps are gill nets with a mesh size of a=90-100 mm. Originality. General trends in the dynamics of integral characteristics of the commercial stock of silver and bighead carps were determined in the context of the scientific fundamentals of managing the biomass of biological control agents. The knowledge on the methodological principles of ensuring the effectiveness of biological amelioration of technical water bodies has been deepened. Practical value. The results obtained were used to adjust the procedure for fishery exploitation of the Khmelnitsky NPP pond in order to implement biological amelioration through the directed development of ichthyofauna. Keywords: Cooling pond, ichthyofauna, biological amelioration, Chinese carps.