Growth potential of sterlet (Acipenser ruthenus Linnaeus, 1758) during the juvenile period using the probiotic preparation “Emprobio”

Purpose. To study the effect of the complex probiotic “Emprobio” on the survival and growth rates of larvae and fry of the sterlet (Acipenser ruthenus) as well as to assess its effect on the morphological structure of the intestine and liver. Methodology. The study of the effect of the probiotic was carried out on larvae and fry of sterlet. 6-hour enrichment of live feed organisms was carried out in 2 variants. In the variant 1, the concentration of the probiotic preparation was 0.4 cm3/dm3 of the incubation mixture. In the variant 2, similarly, the preparation concentration was 4.0 cm3/dm3. Larvae and fry were fed with Artemia nauplii, which were the transfer of the probiotic. Determination of unicellular fungi was carried out by the method of serial dilutions of intestinal contents in a peptone-buffer solution with subsequent inoculation on a sterile wort-agar medium. Light-optical examination of cells and tissues was carried out in penetrating light using the equipment “E. Leitz “diaplan” Wetzlan” (Germany), halogen illuminator “Linvatec-2” (USA). General morphometric studies of tissue structures were performed with the help of a built-in eyepiece-micrometer as well as with the use of an eyepiece-micrometer overlay grid (eyepiece 7x (Huygens). In-depth studies of individual tissue areas were carried out using a 100x objective, “I-Plan” with a built-in iris diaphragm of 5.5 units of a compensation 20x eyepiece “K. Zeiss”. The data were statistically processed in MS Excel. Findings. During the 1st 7 days of the experiment, there were no significant differences in the growth rate of larvae between the groups.In the 2nd week of the experiment, an increase in the average daily weight gain of fish was observed in the experimental groups, which exceeded the control by 47.0% and 24.7%, respectively.At the end of the experiment, the average weight of fry of the 1st group was higher by 26.9%, and of the 2nd — by 27.9%, compared to the control group. As a result of the use of the probiotic preparation for 28 days, the survival rate of sterlet juveniles in the 1st experimental group was 75.0%. That is, it was 47.1% higher than the results of the control group. In the 2nd experimental group, the survival rate of sterlet juveniles was 80.1%, which was 6.8% higher than in the 1st group, and 57.1% higher than in the control group. The use of “Emprobio” in the feed at a concentration of 4.0 cm3/dm3 contributed to a faster process of microflora redistribution in the intestine. Therefore, already after the 1st 5 days of exogenous feeding, the average daily growth rates of the juveniles in this experimental group had higher values (by 8.8%) compared to the control group. The results of inoculation the intestine contents in the experimental groups showed that the use of the probiotic preparation in the incubation mixture in the amount of 0.4 cm3/dm3 ensured the inoculation of probiotic lactic acid bacteria in the intestines of sterlet juveniles. Their functioning was reflected in fish productive parameters, starting from the 14th day of the experiment. However, the lack of intestinal inoculation by one of the components of the preparation, namely saccharomycetes, indicated the insufficiency of such a concentration to show the full potential of the probiotic. In the 2nd experimental group, positive growth dynamics of the entire microbiome can be seen. Histological studies showed a positive effect of the probiotic preparation at a concentration of 4.0 cm3/dm3 on the morphological structure of the liver. In particular, the area of hepatocytes, which increased by 42.9% after 7 days of the experiment and by 63.0% after 21 days of the experiment. The sizes of the nuclei and the ratio of the diameter of the nucleolus/nucleus of hepatocytes also increased. At the same time, the probiotic did not cause probable changes in the morphological structure of the intestinal wall.