Efficiency of growing sturgeon (Acipenseridae) fish species juveniles under different water hardness
Authors:   Lviv Research Station of the Institute of Fisheries NAAS, Velykyj Lubin, Zabytivskyi Yu. , Dobryanska O. ,   Lviv Research Station of the Institute of Fisheries NAAS, Velykyj Lubin, Tuchapskyi Ya. ,   Institute of Fisheries NAAS, Kyiv, Korilyak M. ,   Transcarpathian Research Station of the Institute of Fisheries NAAS, Mukacheve, Yurchak S. ,   Lviv Research Station of the Institute of Fisheries NAAS, Velykyj Lubin
Published: December 2023

Purpose. To evaluate the influence of water hardness on productive parameters when growing sterlet and Russian sturgeon juveniles to viable stages as well as on the formation of the leukocyte formula. Methodology. The study was conducted on larvae and juveniles of sterlet (Acipenser ruthenus Linnaeus, 1758) and Russian sturgeon (Acipenser gueldenstaedtii Brandt & Ratzeburg, 1833).Sturgeon prelarvae and larvae were reared in recirculating aquaculture systems (RAS) at the Lviv research station of the Institute of Fisheries of the National Academy of Agrarian Sciences (NAAS). During cultivation, the main productive parameters were studied, including: average weight, body length, growth rates, mortality, yield from each stage of growing. Water from a well and rainwater were used to prepare three experimental environments, which differed in hardness (within the standard values for sturgeons). In the first variant, the total hardness was 2.5 mg-eq/dm3, (1.25 mmol/dm3), in the second — 4.0 mg-eq/dm3 (2.0 mmol/dm3) and 6.4 mg-eq/dm3 (3.2 mmol/dm3) — in the third. Experimental groups No. 1–No. 3 were created from sterlet larvae placed for growing in three experimental environments, while groups No. 4–No. 6 were from Russian sturgeon larvae grown in similar conditions. Control of hydrochemical parameters was carried out in the certified laboratory of the Lviv Research Station of the Institute of Fisheries of the National Academy of Sciences according to generally accepted methods [2]. The leukocyte formula was determined according to the method described by N.T. Ivanova in the author’s modification. Blood smears were stained with Eosin methylene blue according to May-Grunwald [13]. All data were statistically processed in Statistica 6.0 and MS Excel. Findings. A difference in the results of growing sterlet and Russian sturgeon in water with experimentally created different hardness has been shown. It was found that the optimal environment for growing sterlet is water with a hardness of 4.0 mg-eq/dm3. After 14 days of growing, the average weight of sterlet grown in this water was 1.3 times higher than in the experimental group of fish No. 3, and 2.1 times higher than in the experimental group compared to group of fish No. 1. After 21 days of the experiment, the growth trend was maintained: the average weight of the fish of this group was 1.5 times higher than that of the experimental groups No. 1 and No. 3. After 28 days of cultivation, the average weight of the sterlet in group No. 2 was 1840.00±0.210 mg, and was higher than in groups No. 3 and No. 1 by 1.8 and 1.4 times, respectively. Cumulative mortality in all sterlet groups during the experiment ranged from 8.00 to 11.00%. No significant difference in this parameter was found between the groups, although the tendency towards increased vitality was preserved in group No. 2. Analysis of blood smears after 28 days of cultivation showed a slight difference in the leukogram of the experimental groups. In the peripheral blood of experimental group No. 1 during 21 days of cultivation in “very soft” water (2.5 mg-eq/dm3), a 15% higher count of immature lymphocytes was found than in groups No. 2 and No. 3. Also, in group No. 2 there was a tendency to increase the count of erythroid cells. It has been found that in juvenile starlet grown in “very soft” water, the differentiation of cells of the lymphocytic line occurred a little longer, which was evidenced by the presence of a higher number of lymphoblasts and prolymphocytes. In contrast to sterlet, the highest weight gain in Russian sturgeon during the first seven days of cultivation were observed in group No. 6, which grew in water with a hardness of 6.4 mg-eq/dm3. Their average weight was 29.9% and 13.6% higher than that of fish from the experimental groups No.4 and No.5, respectively, and was 145.26±25.12 mg. The regularity was observed that with the increase in water mineralization, the growth rate of this species increased. At this stage, sturgeons actively fed but their digestive system was not fully developed yet. Mortality was minimal in all groups and averaged 2.0±0.1%. After 28 days of exogenous feeding, sturgeon juveniles in groups No4‒No6 reached the following values: 1525.57±115.47 mg, 1667.74±100.13 mg, and 1824.84±166.51 mg. The difference between the weights of sturgeon No. 4 and No. 5 was insignificant. The highest average weight was achieved in the experimental group No. 6, which was 9.4% higher than the average weight of sturgeons of group No. 5. Cumulative survival in the experimental groups was 79%, 85%, and 75%, respectively. Based on the analysis of blood smears, no significant differences between the experimental groups of fish in the eosinophil count was detected. Actually, eosinophils composed 5-8% of the total count of leukocytes. In group No. 4, similarly to that of sterlet, a high count of immature cells — metamyelocytes — was observed among neutrophilic granulocytes. Their count was inversely proportional to the increase in water hardness. Originality. The advisability of modeling the water environment with the appropriate hardness for rearing various sturgeon species depending on their halophilicity has been demonstrated. The development of the blood leukocyte pattern of sterlet and Russian sturgeon juveniles grown in water with different hardness has been described. Practical value. The obtained results will be useful for improving the technology of early rearing of sturgeon larvae and fry. The application of the acquired knowledge will allow reducing mortality during the critical periods of their cultivation and will allow strengthening the non-specific immunity of these valuable fish species. Keywords: sturgeon, water hardness, viability, leukocyte formula.