ANALYSIS OF THE FOOD SUPPLY OF THE KHRYSTOFORIVSKE RESERVOIR (BOKOVENKA RIVER, DNIPRO CATCHMENT) AND ITS BIO-PRODUCTION POTENTIAL FOR FISHERY EXPLOITATION.

Purpose. Analysis of obtained data and integration of previous hydroecological data and statistical information for the preparation of scientific and biological rationale and development of the regime for rational and environmentally sustainable fishery exploitation of the Khrystoforivske Reservoir. Methodology. Hydrochemical and hydrobiological methods of sampling, laboratory and statistical processing of the material were used in the water area of the Khrystoforivske reservoir of the Bokovenka river during comprehensive studies in the summer of 2022. We studied the hydrochemical parameters of the water body, species composition, quantitative parameters of the main groups of hydrobionts, including fish forage organisms (macrophytes, phytoplankton, zooplankton, zoobenthos), the biological productivity of the reservoir was measured based on the main groups of hydrobionts. To determine the state of the main groups of hydrobionts, two samples of phytoplankton, zooplankton and zoobenthos were collected. Macrophytes were studied, water samples were taken from different parts of the water body for hydrochemical analysis. The biomass of phytoplankton was calculated based on the biomass of standard volumes of algae, the biomass of zooplankton - by multiplying the quantity of organisms by their individual weights, zoobenthos - by weighing individual groups of hydrobionts on torsion scale and recalculating and summing up. The reservoir feeding capacity was assessed by the quantitative development of zooplankton according to known classifications. Findings. The main parameters of the chemical composition and properties of the water of the Khrystoforivske reservoir, which condition the bioproductivity and fish farming performance, were determined: pH, content of dissolved gases, organic substances, biochemical demand of O2, nutrients content, as well as general mineralization and hardness, concentration of the major ions. According to the hydrochemical classification, water is bicarbonate type II and is referred to fresh water. The degree of water saturation with easily-oxidizable organic matter has decreased over the past 15 years and is within standards for aquaculture. Considering all environmental and sanitary parameters, water of the Khrystoforivske reservoir is characterized by fair or average quality, it is eupolytrophic. The water characteristics indicate that the fishery exploitation at the reservoir during previous Special Commodity Fish Farming Regimes (SCFF) (1996-2021) has produced no adverse effects on the general ecological and sanitary condition of water. Aquatic phytocoenoses of the Khrystoforivske reservoir are represented by associations of submerged and aerial-aquatic plants, with a total area of 5.2 hectares. The total production of aquatic plants is 36.245 tons. The phytoplankton of the reservoir includes 51 species of algae (six groups). In terms of quantity, small-celled Cyanoprokaryota predominated (about 70%). Diatoms, green and euglenic algae dominated in biomass. In 2022, the average biomass of phytoplankton in the Khrystoforivske reservoir was up to 1.80 g/m³, the total annual production of phytoplankton reached 201.06 tons. In total, 16 species of organisms have been identified in the zooplankton of the reservoir: Rotatoria, Cladocera and Copepoda. The average abundance of zooplankton in the reservoir was 31,390 ind./m³, and its average biomass reached 0.41 g/m³. The value of primary production of zooplankton is 123.9 kg/ha, and the total stock in the reservoir is 7.687 tons. The fish food supply in terms of zooplankters in the Khrystoforivske reservoir are low. The reservoir itself, based on the group of zooplankton, can be referred to fishery class III (the lowest class). The bottom fauna is represented by 40 taxonomic groups of invertebrates. The Chironomidae and Oligochaeta assemblies are most developed in terms of density, but molluscs dominate in biomass. There is a general trend towards a decrease in the quantitative parameters of macrozoobenthos, in particular, Mysidacea. The average biomass of soft benthos (2.17 g/m²) and the average biomass of the entire zoobenthos (33.62 g/m²) indicate that the reservoir preserves its fishery potential due to macrozoobenthos. The primary production of zoobenthos of the Khrystoforivske reservoir is 130.2 kg/ha. The total stock of zoobenthos is up to 8.072 tons. The values of the fish food supply are quite high due to zoobenthos in the reservoir, the water body in terms of benthos biomass is referred to fishery class II (medium productive reservoirs). The obtained comprehensive data on the food supply of the Khrystoforivske reservoir indicate the availability of sufficient bioproduction potential for its continuous effective fish-farming on the basis of the special commodity fish farming regime. Originality. For the first time in the last 10 years, comprehensive data on the food supply of the Khrystoforivka reservoir, which is used in special commodity fish farming regime (SCFF), have been obtained and analysed. Practical value. The results obtained are of practical importance for the development of scientific and biological rationale for fish farming in the Khrystoforivske Reservoir. [ABSTRACT FROM AUTHOR]