There is a possibility of developing a pathological process in the body of fish in the conditions of high-tech industrial aquaculture and at high planting densities, creating chronic stress. Histological studies allow early detection of the initial stages of possible pathology at the cellular level. The studies have shown that apparently healthy individuals of African catfish grown in recirculating aquaculture systems (RAS) revealed pathology of cells and tissues of the gastrointestinal tract. They had edema of the internal muscle layer of the stomach and intestines, detachment of the epithelial layer from the gastric mucosa, violation of the structural organization of gastric fields on histological sections. Thinning of intestinal villus, reduction of their length and branching, violation of their structure up to destruction were also revealed. The study of the tissues of the stomach and intestines was carried out using a research motorized universal microscope Axio Imager.M2 (Carl Zeiss, Germany). To correct the pathological process, the experimental group of fish received a “sporothermin” probiotic with feed, which belongs to the probiotics of the last generation. It is an antagonist of a wide range of pathogenic and opportunistic microbiota and is used as an alternative to antibiotics. The composition of “sporothermin” includes spore forms of bacteria Bacillus subtilis and Bacillus licheniformis, which in the gastrointestinal tract of fish turn into vegetative forms. Bacteria Bacillus subtilis and Bacillus licheniformis are not representatives of the intestinal microbiocenosis of the African catfish, but they regulate its structure by reducing the level of pathogenic and opportunistic microbiota. Pathology of cells and tissues of the gastrointestinal tract have been identified in the fish of the experimental group treated with the sporothermin probiotic.

This article is devoted to the study of the qualitative and quantitative characteristics of the African Catfish Clarias gariepinus eggs produced at different durations of the inter-spawning interval. Eggs were produced artificially using sex hormones. In industrial aquaculture, the African Catfish Clarias gariepinus does not reproduce naturally. Therefore, the problem of obtaining high-quality eggs that will be used for in-vitro fertilization is urgent. To implement artificial spawning of fish in industrial aquaculture, it is necessary to correctly choose the effective hormonal stimulator and empirically select its dose. Sex hormones are involved in regulating the duration of the inter-spawning interval and affect the quality of eggs produced both for fertilization and for food purposes. The pituitary gland of the African Catfish Clarias gariepinus and surfagon were used as gametogenesis stimulators. The aim of the work was to study the optimal duration of the inter-spawning interval and the effect of hormonal inducers used to stimulate artificial spawning in industrial aquaculture. The use of the catfish pituitary gland in fresh or acetonated form as a hormonal stimulator provided higher-quality eggs, compared to the synthetic hormonal drug - surfagon. Stimulation with acetonated pituitary injections reduced the inter-spawning interval of the African Catfish Clarias gariepinus to three months, and the use of surfagon prolonged the inter-spawning interval to four months. Reducing the duration of the inter-spawning interval is important for the production of the African Catfish Clarias gariepinus eggs for food purposes. Studies have shown that reducing the optimal duration of the inter-spawning interval negatively affects the quality of the produced eggs and their quantity. This research was financially supported by a grant from the Russian Foundation for Fundamental Research, project No. 18-016-00127. Keywords: aquaculture, African Catfish Clarias gariepinus, eggs, inter-spawning period, sex hormones, oocytes

When growing fish in high-tech breeding systems, it is exposed to many stress factors. To reduce stress, we used spore forms of microorganisms — Bacillus subtilis and Bacillus licheniformis, possessing probiotic properties. Two groups were formed, a control group and an experimental group that received probiotic microorganisms with feed. The aim of the study was to evaluate the effectiveness of the use of microorganisms — Bacillus subtilis and Bacillus licheniformis to reduce stress in fishes. For this indicator points were selected — stress hormone cortisol and antioxidant defense enzymes. The research results showed that stress level assessed by cortisol in fishes fed with probiotic microorganisms is 2.8 times lower than in the control group. The use of micronucleus test to assess cytogenetic damage showed that against the probiotic microbiota background, the number of cells with fragmented nuclei decreases by 5.7 times. Antioxidant defense enzyme activity when using Bacillus subtilis and Bacillus licheniformis increased, indicating activation of the defense system against oxidative stress. The obtained results demonstrated the high efficiency of the use of spore forms Bacillus subtilis and Bacillus licheniformis when growing catfish in high-tech fish farming systems. The Russian Foundation for Basic Research has supported our study with the grant No. 18-016-00127.

In different periods of the life cycle, the chemical composition of fish muscle tissue is subject to significant fluctuations. These changes are most pronounced during the spawning period, when there is a switch to generative exchange. The studies of the nutritional value of the meat of African catfish (Clarias gariepinus) in the spawning period showed that the protein content of this species of fish falls into the category of protein products containing a full range of essential amino acids; by the fat content in muscle tissue, it can be attributed to the varieties of fatty fish. According to the research, the muscle mass of this fish species contains high levels of mono - and polyunsaturated fatty acids and is characterized by high levels of linoleic acid, which is an essential fatty acid. The content of linoleic acid in the muscles of African catfish is much higher than in the muscles of pink salmon. The content of linoleic acid in the caviar of African catfish is seven times higher than in the caviar of pink salmon. African catfish caviar also contains a large amount of oleic acid, which plays an important role in the prevention of cardiovascular diseases. The results showed that during the spawning period, the nutritional value of the muscle tissue of the African catfish remains high. The results of the study are important for the development of African catfish caviar production and give a positive answer to the question whether it is possible to obtain edible caviar from catfish without compromising the production of commercial fish of high nutritional value.

The article presents the results of the analysis of the content of vitamins in the meat of the African catfish Clarias gariepinus from the Clariidae family, which are widespread in the world’s industrial aquaculture. Studies have shown that African catfish meat contains water- and fat-soluble vitamins. Fat-soluble vitamins are represented by vitamins A and E. The group of water-soluble vitamins consisted of vitamins PP, C, and B vitamins (B1, B2, B5, and B6). Studies have shown that the meat of the studied fish species has a high biological value. It contains functional food ingredients - vitamins A, PP, B1, B5, B6 in an amount of at least 15% of the daily physiological requirement. According to the results obtained, the content of all water-soluble vitamins in the muscle tissue of males exceeds that of females. During the study, it was revealed that the introduction of the probiotic Sporothermine into the fish diet based on the spore forms of the bacteria Bacillus subtilis and Bacillus licheniformis causes a significant increase in the content of some vitamins. In particular, the content of vitamins B5, B6, nicotinic, and ascorbic acid increases. Fat-soluble vitamins showed increased content of vitamin E.