Effect of the complex of probiotic microorganisms of the genus Bacillus on the growth, histological structure of intestines and the resistance of sturgeon hybrid juveniles
Authors:   Lviv Research Station of the Institute of Fisheries NAAS, Velykyj Lubin, Zabytivskyi Yu. , Tuchapskyi Ya. ,   Institute of Fisheries NAAS, Kyiv, Dobryanska O. ,   Lviv Research Station of the Institute of Fisheries NAAS, Velykyj Lubin, Boretska I. ,   Lviv Research Station of the Institute of Fisheries NAAS, Velykyj Lubin, Vishchur O. ,   Institute of Animal Biology NAAS, Lviv
Published: October 2024

Purpose. The purpose of this work is to evaluate the effect of a complex of probiotic microorganisms from the genus Bacillus, namely Bacillus subtilis, B. pumilus, B. licheniformis and B. amyloliquefaciens, as part of the Sviteco-“PWS” preparation, on the growth potential, survival rate, intestinal histostructure and non-specific resistance of age-0+ hybrid sturgeon. Methodology. The object of the study was hybrid juveniles obtained from ♀ bester (♀ Huso huso × ♂ Acipenser ruthenus) and ♂ sterlet (Acipenser ruthenus) (BSS), which were reared in recirculation aquaculture system (RAS) tanks at the Lviv Research Station of the Institute of Fisheries of the National Academy of Agrarian Sciences. The initial weight of the juveniles was 30.69±1.12 g, the stocking density was 30 ind./m2.The duration of the experiment was 28 days. The preparation of the working solution of the “PWC” probiotic complex was carried out by diluting 0.7 dm3 of the preparation concentrate in 50 dm3 of water at a temperature of 35°C. Before feeding, the solution was applied by spraying in an even layer on the feed for the experimental group of fish at the rate of 50 dm3/kg of feed. During cultivation, such fish productive parameters as growth rate, feed conversion ratio and survival rate were periodically studied. At the end of the study, the lysozyme activity of the blood serum was also determined by the nephelometric method, the composition of the intestinal microbiota — by the deep inoculation method, and the histostructure of the medial part of the intestine was studied using light microscopy. The obtained data were processed by variational statistics using MS Excel and Statistica 12.0. The probability of a difference in the results was determined using a one-way analysis of variance (ANOVA) with Tukey’s test. Findings. The positive effect of the probiotic complex was observed in the first 7 days. Next, the fish body used nutrients with approximately the same efficiency in both experimental and control groups and developed linearly. At the end of the experiment, the average weight of sturgeons in the experimental group was 9.57% higher than in the control group (p<0.05). In addition, the growth rates of fish from the experimental group were naturally higher in the first week of experimental feeding and amounted to 6.43±0.14%/day, which was 1.7 times higher than the control. The average daily growth rate during the experimental period in the experimental and control groups was 3.87±0.42%/day and 3.55±0.14%/day, respectively. In the first week of feeding with the probiotic preparation, the average daily growth rate (ADGR) of the experimental individuals was on average 72% higher than that of the control group of fish. These initial growth rates subsequently had a significant effect on total weight accumulation, as the average weight of fish from the experimental group remained higher throughout the entire period of the experiment. The analysis of feed conversion rates (FCR) showed that during the first 7 days of using the probiotic complex, feed conversion in the sturgeons of the experimental group was 0.45, and 0.79 in the control group. Thus, the efficiency of feed use will increase by 1.7 times during the first 7 days of feeding. Feed conversion during the next 3 weeks of feeding was 0.75 in both control and experimental groups of fish. It was found that after 28 days of using the PWC probiotic complex, the lysozyme activity of the sturgeon blood serum of the control group was 52.40±1.86%, and that of the experimental group was 54.86±1.56%. A trend towards an increase in lysozyme activity in the experimental group was observed. In addition, members of the genus Bacillus were found in the intestines of the sturgeons from the experimental group as a result of inoculating the intestine contents, which were introduced with the probiotic complex PWC, which were not found in fish from the control group. At the same time, the count of lactobacilli in the intestines of experimental sturgeons was 1.85 (p<0.01) times higher. These changes occurred against the background of a decrease in the count of yeast-like fungi, respectively, by 1.6 times (р<0.05) and an increase in the count of opportunistic E. coli microflora by 1.5 times (р<0.05). As a result of the use of the probiotic complex “PWC”, the height of the folds of the medial part of the intestine tended to increase. Due to this, the thickness of the entire epithelial layer and the total area of ​​the absorptive surface of enterocytes increased. Originality. For the first time, the effectiveness of using a complex of probiotic microorganisms of PWC to improve growth performance and strengthen non-specific resistance of sturgeon juveniles was analysed. For the first time, the effect of the probiotic complex on the lysozyme activity of the blood serum and the histoarchitecture of the medial part of the intestine of the sturgeon hybrid was demonstrated. Practical Value. The obtained results contribute to the improvement of the technology of growing juvenile sturgeons with the use of complexes of probiotic microorganisms of the genusBacillus. The application of these data will allow increasing the productivity of cultivation and obtain a high-quality and healthy stock of sturgeons. Keywords: probiotic, sturgeons, recirculating aquaculture systems (RAS), Bacillus, breeding productivity, non-specific resistance, feed conversion.