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

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. FIn 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.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.