Use of Next-Generation Probiotics in Production Feed for Red Tilapia Yearlings (Oreochromis mossambicus x O. niloticus)

Abstract. The use of next-generation probiotic preparations in the form of biofilm on a solid phyto-substrate in dry compound feeds for red tilapia yearlings has been scientifically substantiated. The most technologically practical approach is to use the dry form of probiotics, as it withstands the processes of granulation, expanding, and extrusion of compound feeds, which facilitates the production of therapeutic and preventive feeds on an industrial scale and simplifies the use of these preparations in aquaculture. The conducted research studied the effect of next-generation probiotic preparations when introduced into production compound feeds for cichlid fish. They had a positive effect on growth, survival, and the physiological state of the fish. The positive effect obtained from the introduction of probiotics in biofilm form into compound feed can be explained by their ability to produce vital digestive enzymes and vitamins directly in the intestine, thereby exhibiting a pronounced growth-stimulating effect. Blood indicators allowed the conclusion that the quality and effectiveness of compound feeds used in combination with probiotic preparations were high. They did not cause deviations in fish health status or metabolic disorders. The greatest positive effect on blood biochemistry was exhibited by the ProStor preparation with phytobiotics.

Keywords: next-generation probiotics, yearlings, red tilapia, compound feed, blood.

Topic Relevance

In modern aquaculture, rational fish feeding plays an important role. The importance of feeding continuously increases with the rising level of intensification of fish farming processes. The use of high-quality and complete compound feeds is of great importance in industrial aquaculture conditions. In addition to the balance of basic nutrients in fish feeds, it is necessary to consider biologically active substances, among which are probiotic preparations that have found wide application in commercial fish farming.

Currently, special attention is paid to next-generation probiotics in biofilm form; however, their effect on fish has been poorly studied. Probiotics in biofilm form on a solid phyto-substrate, with preserved bacterial metabolites and biologically active substances, introduced into feeds for agricultural animals, can significantly improve the health of the animal organism and produce high-quality products.

Materials and Methods

The research was conducted at the Innovation Center "Bioaquapark - Scientific and Technical Center for Aquaculture" of Astrakhan State Technical University. Red tilapia yearlings (Oreochromis mossambicus x O. niloticus) were used as research objects. Fish were reared in 400-liter aquaria with filtration, aeration, and regulated temperature. Water temperature was maintained within 25.3-29.6 °C. Oxygen content was not below 6.2 mg/L.

Two types of probiotic preparations were used for experimental work: ProStor and Ferm-KM, produced by LLC NTC BIO (Russia). The preparations include probiotic bacteria - strains of Bacillus subtilis and Bacillus licheniformis, immobilized in biofilm form on specially prepared beet pulp. ProStor additionally contains phytobiotics of medicinal plants (milk thistle and Echinacea purpurea).

Research was conducted under laboratory conditions over 14 days. Fish were divided into experimental groups and a control: in the 1st experimental group, feeding was carried out with compound feed (ASTU formulation) with the addition of the ProStor probiotic; in the 2nd group - with the addition of the Ferm-KM probiotic. The dry form of probiotics was introduced into compound feeds during manufacturing at a rate of 2.0 kg/t of compound feed.

Water temperature and oxygen content were determined daily using a thermo-oximeter "OXYGUARD Handy Polaris" (Denmark); pH level was measured using a portable pH meter "Checker-1" (Germany). For hematological studies, blood was collected from the caudal artery using a medical syringe.

Research Results and Discussion

During the research period, weight gain was observed in both control and experimental variants; however, when rearing on experimental compound feeds, it was higher than in the control group. Survival was 100% in all variants.

Based on rearing results, the best aquaculture-biological indicators were noted for both experimental groups of fish consuming compound feed with probiotic additives, compared to control fish. During the rearing period, absolute weight gain in experimental groups was 11.0-11.8 g, which is nearly twice as high as in the control. The highest indicators of average daily weight gain (0.79-0.84 g) and average daily growth rate (1.22-1.52%) were also characteristic of yearlings reared on feeds with probiotics.

The data obtained during the rearing period allow the conclusion that the introduction of next-generation probiotic preparations into production compound feeds is effective, as they promote the production of vital digestive enzymes and vitamins directly in the intestine, thereby expressing a growth-stimulating effect.

Assessment of the physiological state of fish was performed based on hematological parameter analysis of red tilapia yearlings. Studies showed that experimental variants had better blood indicators. Total protein concentration in both control and experimental variants fluctuated within the lower boundary of the norm characteristic for fish from natural water bodies (20-40 g/L). The relatively low level of total protein is often observed in tilapia reared under industrial conditions. This may be related to both feeding specifics and the level of stress load that is always present when keeping fish in ponds or pools. This leads to excessive expenditure of protein, an easily metabolized biochemical substrate. Additional energy in this case is used to overcome stress. The presence of a stress situation is confirmed by elevated cholesterol levels in the blood of fish, to a greater extent in the control (3.6 mmol/L). In experimental fish, this indicator was 1.7-2.4 mmol/L. If cholesterol is considered as a biochemical component facilitating fish overcoming stress loads, then the decrease in cholesterol levels in experimental fish indicates an increase in their stress resistance.

Total lipid concentration in the blood during the research period in fish of different variants was 3.89-4.22 g/L for experimental groups and 5.56 g/L for the control group, which practically corresponded to the norm. This allows the conclusion that the direction of fat metabolism in these fish promoted normal accumulation of energy resources. The main indicator of lipid metabolism intensity is the level of triglycerides in fish blood. For tilapia, this indicator should be 1.43-1.46 mmol/L. In the control group, triglyceride concentration was 2.9 mmol/L, which apparently contributed to the elevated blood lipid content (5.56 g/L). In experimental groups using probiotic preparations, the triglyceride level did not exceed 0.81 mmol/L.

Erythrocyte sedimentation rate (ESR) has diagnostic significance; for fish it corresponds to 2-10 mm/h. In all variants, this indicator did not exceed 4.33 mm/h, indicating the absence of inflammatory processes. Hemoglobin levels in fish blood ranged from 88.8 to 142.5 mg/L; the maximum indicator was characteristic for yearlings of the 1st experimental group (ProStor probiotic). Blood glucose levels in red tilapia yearlings in both control and experimental groups fluctuated from 3.33 to 3.7 mmol/L and did not exceed normative indicators.

Conclusion

Thus, the data obtained during the conducted research allow the conclusion that the use of next-generation probiotic preparations in production compound feeds for cichlid fish is effective, as they promote improved growth indicators, reduce feed costs, and maintain the physiological state of fish at levels corresponding to the norms.

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