Purpose. Determination of the biological effect of milk thistle oil at different amounts of its introduction into the diet (0.5, 1.0 and 1.5%) on the antioxidant status of the body of juvenile carp in the conditions of recirculating aquaculture systems. Methodology. For the experimental studies, 4 groups of juvenile carps were formed, 150 individuals in each, with an average weight of 0.012 g, which were kept in 150 dm3 tanks with artificial water aeration. The period of their adaptation to holding conditions lasted 7 days. Over the next 21 days, the fish of the control and experimental groups were fed with compound feed with a protein content of 23%. The daily feed of fish of the experimental groups were additionally supplemented with milk thistle oil at amounts of 0.5 (Experiment I); 1.0 (Experiment II) and 1.5% (Experiment III). The juveniles were fed with the addition of oil three times a day. At the end of the experiment, skeletal muscle samples of juveniles were taken for the biochemical study. The concentration of diene conjugates was studied by the method based on the reaction of the optical density of the heptanisopropanol extract of lipids. Determination of the concentration of TBC-active products was carried out spectrophotometrically by a color reaction with thiobarbituric acid. The activity of superoxidedismutase was determined by the percentage of inhibition of the reduction reaction of nitroblue tetrazolium in the presence of phenazine metasulfate. Catalase activity depended on the change in the concentration of hydrogen peroxide (H2O2). Protein content was determined by the Bradford method. Processing of experimental results was carried out by the method of variational statistics. A statistically significant difference in obtained values was assessed by the Student’s t-test. Findings. It was found that the main parameters of water quality were within the normal values and the environment during the cultivation of the young-of-the-years was optimal. A positive effect of the use of milk thistle oil on the average weight was noted, which exceeded the average weight of fish of the control group by 3.8; 11.5; 7.8%. The survival rate of the fish of the experimental groups was higher in Experiment II and Experiment III by 7.4; 4.9% relative to the control group. An increase in superoxidedismutase activity was observed in all experimental groups, namely in Experiment I by 20.0%, Experiment II and Experiment III by 55.0% and 57.0% (p<0.01), respectively. At the same time, a decrease in the intensity of lipid peroxidation processes was observed in all experimental groups of fish. It was found that the addition of 1.0 and 1.5% milk thistle oil to the diet of juvenile carps had a positive effect on productive and biochemical parameters of their body. Originality. For the first time, the optimal norms for the introduction of milk thistle oil into the daily diet of juvenile carps and the effect of feeding this phytosupplement on the activity of antioxidant enzymes and the content of products of lipid peroxidation were determined. Practical value. The obtained results indicate the advisability and effectiveness of using milk thistle oil as a phytoaddition in growing and feeding juvenile carps. Keywords: juvenile carp, milk thistle oil, antioxidant enzymes, content of lipid peroxidation products, weight gain, survival rate.
