Effect of hydrochemical parameters of ponds on the quality of fish seeds in the conditions of the Kherson industrial and experimental hatchery for growing common freshwater fish

Purpose. To analyze the effect of the main hydrochemical parameters in the nursery ponds of the Kherson production and experimental hatchery for the cultivation of common freshwater fish on the quality of fish seeds. Methodology. Studies of hydrochemical parameters of the first-order nursery ponds (No. 2, 3, 9, 10, 11, 12, 13, 15, 16) were carried out at the Kherson production and experimental hatchery for the cultivation of common freshwater fish. Collection of hydrochemical water samples was carried out during the growing season of 2021 from spring to autumn. During the study, a total of 81 samples were processed in 9 ponds (an integrated sample from three sites of the pond) according to 14 physicochemical parameters, which included the gas regime, physical properties, mineral and ionic composition of water, the content of biogenic, organic and specific pollutants. Chemical analysis of water samples was performed in the field with a Palintest 7100 multiparametric photometer and the laboratory of the Kherson State Agrarian and Economic University, Department of Water Bioresources and Aquaculture. Concentrations of oxygen, free hydrogen ions and water temperature were determined with a portable multimeter AZ86031. The fish seeds were studied to determine the average weight, linear growth, gut fullness index, and Fulton’s condition factor. The material was processed in a quantitative-weight way by individual review of digestive tracts. At the same time, fat content, color of food, degree of gut fullness was determined. Findings. The article examines the effect of the hydrochemical regime of the ponds of the Kherson production and experimental hatchery for the cultivation of common freshwater fish on the quality of fish seeds. The main hydrochemical parameters of nursery ponds, growth, length and weight parameters, gut fullness index, Fulton’s condition factor during the cultivation of fish seeds were analyzed, and an assessment of these parameters was carried out. It was established that the water in the ponds throughout the year was significantly saturated with organic and biogenic substances. In a number of ponds, an excess of bichromate oxidation, biological oxygen consumption, and periodically - permanganate oxidation was constantly recorded. The peak of organic water pollution falls on the summer-autumn period. At this time, the content of nitrogen-containing compounds, phosphates, and total iron increased, water bloom was observed, and cases of dissolved oxygen deficiency were recorded, which negatively affected the quality of fish seeds – silver and bighead carps. The main cause of oxygen deficiency is its active consumption by hydrobionts and costs for the oxidation of organic substances in water. The dynamics of the increase in the total mineralization of water in the ponds from spring to autumn were monitored. The natural genesis of this process has been established and the possible risks that may arise during the cultivation of fish seeds in connection with the specified dynamics of mineralization throughout the year have been assessed. As a result of the cultivation of fish seeds according to length and weight parameters, the index of gut fullness and fatness, a decrease in the intensity of growth and weight gain of silver and bighead carps was established, their values at the end of October were within the normative limits - 20 g (l = 11.56 cm, Q = 20.18 g), while the increase in almost three months (August - October) amounted to only 5 g. The reason for this is a decrease in the general index of gut fullness from June to September, respectively, these values in July averaged 129.250/000, in August there was a decrease to 91.90/000, in September the lowest va.ue was 500/000 The condition factor reflected a similar situation, a decrease from mid-summer to late September ranging from 1.64 to 1.30. This phenomenon indicates low feeding activity in this period, which we associate with the deterioration of the hydrochemical state of the water in the nursery ponds. Originality. Modern data on the main parameters of the hydrochemical regime of nursery ponds are presented. The relationship between organic pollution in the summer-autumn period, an increase in the content of nitrogen-containing compounds, phosphates, total iron, a deficiency of dissolved oxygen and the quality of fish seeds was established. The obtained results demonstrate the actual values ​​of the hydrochemical state of the studied objects, in particular, the oxygen regime of the ponds has dynamics opposite to the dynamics of the content of organic substances. Practical Value. The analysis of the dynamics of the most significant elements of the hydrochemical regime of nursery ponds and the establishment of a close relationship between it and the phases of the technological processes of growing fish seeds leads to the shortening of the cycle of cultivation. Considering the tendency a decrease in the condition factor and gut fullness index from mid-summer of all cultivated fish species, there is a proposal to reduce the technological cycle of growing fish seeds until the end of August, when common and grass have values within the standard at the level of 22.68 g for grass carp, 35.18 g for common carp, while silver and bighead carps below normative values at the level of 15.0 g. Such a reorientation will allow reducing the costs of growing fish seeds by almost three months and to carry out the introduction in the period when it has the best adaptation and compensatory indicators.