In this, work some aspects of the development of the visual system of Nothobranchius guentheri at the main stages of ontogenesis were described for the first time. It was possible to establish that the formation of the visual system occurs similarly to other representatives of the order Cyprinodontiformes, but significantly differs in terms of the individual stages of embryogenesis due to the presence of diapause. In the postembryonic period, there is a further increase in the size of the fish’s eyes and head, to the proportions characteristic of adult fish. The histological structure of the eye in adult N. guentheri practically does not differ from most teleost fish living in the same environmental conditions. The study of the structure of the retina showed the heterogeneity of the thickness of the temporal and nasal areas, which indicates the predominant role of peripheral vision. Morphoanatomical measurements of the body and eyes of N. guentheri showed that their correlation was conservative. This indicates an important role of the visual system for the survival of fish in natural conditions, both for the young and adults. In individuals of the older age group, a decrease in the amount of sodium (Na) and an increase in magnesium (Mg) and calcium (Ca) were found in the eye lens. Such changes in the elemental composition of the lens can be a sign of the initial stage of cataractogenesis and disturbances in the metabolism of lens fibers as a result of aging. This allows us to propose N. guentheri as a model for studying the structure, formation, and aging of the visual and nervous systems.

This article presents data on the species composition of periphyton organisms in biofilms of cold-water biological filtration systems intended for the cultivation of rainbow trout (Oncorhynchus mykiss) and warm-water species for the cultivation of (Clarias gariepinus) in a recirculating aquaculture system. Data on the occurrence of certain groups of periphyton organisms are presented, and their role in the process of water purification is indicated. A significant difference in the species composition of biofilter biofilm organisms is shown, depending on: temperature regime and planting density of aquaculture objects. The species composition of aquasysets is similar to that in urban wastewater treatment systems.

In this study, the effect of three promising feed additives (chelated compounds of trace elements, butyric acid, lycopene) on changes in the culturable microbiota and histological parameters of two sections of the intestines of Danio rerio (zebrafish) was studied. The use of these feed additives can help to eliminate the deficiency of trace elements, modulate the composition of the microbiota due to the postbiotic properties of butyric acid, and reduce oxidative stress when using lycopene. Incorporation of the investigated supplements in the feed resulted in a significant change in the relative abundance of certain groups of microorganisms. The taxonomic diversity of cultured microorganisms did not differ in the anterior and posterior intestines, while there were differences in the relative abundance of these microorganisms. The most sensitive groups of microorganisms were the genera Bacillus and Serratia. A significant effect on the composition of the cultured microbiota was caused by lycopene (in all studied concentrations), leading to a significant increase in the relative abundance of Firmicutes in the anterior gut. Studies of the histological structure of the anterior and posterior guts have shown the relationship between the barrier and secretory functions of the gut and the composition of the microbiota while using butyric acid (1 and 2 g kg−1) and trace element chelated compounds (2 mg kg−1). This culture-dependent method of studying the microbiome makes it possible to assess changes in some representatives of the main groups of microorganisms (Firmicutes and Proteobacteria). Despite the incompleteness of the data obtained by the culture-dependent method, its application makes it possible to assess the bioactive properties of feed and feed additives and their impact on the microbiota involved in digestive processes.

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In this paper, the dependence of the temperature conditions of incubation of microbiological water cultures taken directly from the pool of a closed water supply system on the activity and species diversity of the resulting microflora is analyzed. The object of the study was clarias catfish (Clarias gariepinus), which was grown at a temperature of 22-24 °, Ph 6.5-7.5, which corresponds to the optimal requirements for breeding this type of fish. The study was conducted on the basis of the Russian-Norwegian Center for Research in the field of Innovation and Aquaculture of the MSUTM named after K.G. Razumovsky. As a result of the study, a reliable regularity of the activity of aquatic microflora in CFU / ml, as well as generic and species affiliation, was revealed.