Biological peculiarities of the body of juvenile sturgeons (Acipenseridae Bonaparte, 1831) under the action of synthetic and organic immunostimulators

Purpose. To analyze the productive-biological and biochemical parameters of sturgeon larvae and fry under conditions of introduction of synthetic (Levamisole) and organic (Chitosan) immunostimulants into their diet. To evaluate the effect of supplements on the stability of homeostatic processes based on the analysis of enzyme activity. Methodology. The study was carried out on juvenile hybrid besters (♀ Huso huso х ♂ Acipenser ruthenus) and sterlet (Acipenser ruthenus) (BSS). Larvae and fry were fed with Artemia nauplii, which were the transfer of immunostimulants after a six-hour enrichment in the respective solution. Pre-larvae, larvae and fry of sturgeon were reared in a RAS at the Lviv Research Station of the Institute of Fisheries of the National Academy of Sciences of Ukraine. During cultivation, the main productive parameters were studied, which included: weight, body length, growth rates, mortality, output from each stage of cultivation. The activity of α-amylase was determined by the Karavey's method. Alanine aminotransferase activity was determined by the Reitman–Frenkel's method. Alkaline phosphatase activity was determined by reaction with phenylphosphate. Gamma-glutamyltranspeptidase activity was determined by reaction with L-gamma-glutamyl-p-nitroaniline. All data were statistically processed using Statistica 6.0 and MS Excel. Findings. Addition of Levamisole to the diet during the first week of exogenous feeding had a positive effect on the growth processes of sturgeon larvae. The average weight of experimental fish in the experimental group No. 1 increased during the week by 3.96 times, which was 9% higher than the control values. In the experimental group No. 2, which consumed Chitosan, no significant difference was found compared to the average weight of the control group. Average daily growth was 24.9% in the experimental group No. 1 and 20.7% in the group No. 2, and 22% in the group No. 3, which served as a control. After 21 days of the experiment, the average body weight of juvenile sturgeons in the group No. 1, which consumed Levamisole, increased to 0.794 g, which exceeded the control values by 50.5%. The average weight of juveniles in the experimental group No. 2 was 0.661 g, which was 25.28% higher than the control group. The average growth rates were 9.3% in the group No. 1, 12.1% in the group No. 2, and 11.3% in the group No. 3. The short-term positive effect of immunostimulants on the activity of digestive enzymes of sturgeons in the juvenile period was shown. The activity of α-amylase in the body of fish for 21 days under the action of both Levamisole and Chitosan was higher than in the control by 88.2 and 91.4%, respectively. The analysis of the effect of immunostimulants on the activity of transferases (AlAT, LF, GGTP) of the tissues of internal organs confirmed the strengthening of the nonspecific resistance of the body in the short period of their action due to the activation of the transport processes of dephosphorylation and transamination. In addition, the activity of none of the enzymes indicated the impairment of homeostasis. Originality. The advisability of using synthetic and organic immunostimulants in raising sturgeons has been demonstrated. The effect of these supplements on the productive and biochemical parameters of juvenile sturgeons was evaluated. 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 critical periods of their cultivation and will allow strengthening the non-specific immunity of these valuable fish species.