The effect of probiotic-enriched feed on aquaculture-biological parameters of rainbow trout Oncorhynchus mykiss (Walbaum, 1792) during early ontogeny

Background. The issues of increasing productivity in various sectors of agriculture, especially the aquaculture sector, are currently a priority for many research teams in Russia and other countries. The production intensification inevitably leads to a decrease in the resistance of aquaculture objects, which makes them susceptible to various pathogenic agents, resulting in a decrease in overall production efficiency. The use of probiotics in the biotechnological farming cycle can reduce the negative effects of intensification. It has been repeatedly suggested that bacterial strains with probiotic properties, which were originally characteristic of the organism in question and its habitat, have the greatest effect on the fish body. In this paper, the effects of probiotic bacterial strains isolated from bottom sediments in fish habitats are considered.

Purpose. The aim of the study was to study the effect of probiotics in the feed on the fish-breeding and biological parameters of trout Oncorhynchus mykiss (Walbaum, 1792) during the early ontogenesis.

Materials and methods. The experimental site was an industrial-type fish hatchery located in the Rostov region. The object of the study was 100,000 species of O. mykiss rainbow trout larvae aged 29 days, which were randomly divided into 2 groups (control and experiment). The duration of the experiment was 30 days. The diet of the individuals included starter feeds for juvenile salmon with a grain size of 0.2 mm and a crude protein content of 58.0%. The experimental group received a probiotic supplement with 2 strains of the bacterium Bacillus subtilis (strains MT48 and MT74) as a part of the diet. The content of bacterial cells in the finished feed was 7.3·106 CFU/g. The valuation, during which the morphometric parameters of the fish were evaluated, was carried out 2 times during the experiment period: at the beginning and at the end. To assess the effectiveness of probiotic implementation in the diet, fish farming coefficients were calculated: Fulton’s fatness coefficient, individual weight gain, total biomass gain, feed conversion rate and survival rate.

Results. The addition of probiotics based on B. subtilis (strains MT48 and MT 74) to the feed of O. mykiss larvae led to a significant improvement in fish biological parameters. In the experimental group, there was an increase in the average individual fish weight by 12.68% and body length compared with the control group. The survival rate of larvae in the experimental group was higher by 19.41%, and the total increase in biomass increased by 38.31%. The feed conversion rate decreased from 1.69 kg/kg in the control group to 1.04 kg/kg in the experimental group, indicating a more efficient use of feed. The statistical analysis confirmed the significance of the differences between the groups (p<0.05).

Conclusion. The study confirmed the effectiveness of probiotics based on B. subtilis (strains MT48 and MT 74) in feeding O. mykiss larvae. The inclusion of probiotic supplements in the diet contributed to a significant improvement in key fish-breeding and biological parameters: an increase in body weight, length and survival rate and a decrease in feed conversion rate.