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Growing fish in a recirculating aquaculture system (RAS) involves various stress factors that directly affect their physiological condition. This study aimed to investigate the effect of a chelated organic-mineral additive including Fe, Mn, Cu, Zn, Co, Se and I; on the rearing performance of juvenilecatfish (Clariasgariepinus) under RAS conditions. Four groups of fish (n=50) were formed: a control group (receiving standard feed) and three experimental groups (receiving standard feed with biogenic elements chelate compounds in different concentrations). At the end of the experiment (30 days), the physiological condition of the fish was evaluated by the growth rate, internal organs condition, blood serum biochemical indices and histological examination of the middle intestine. The survival rate of fish in the experimental groups was 96-98%. According to the results, the absolute increase was 14,30% in group III, 11,13% in group II and 6,71% in group I, compared to the control. However, the use of chelated compounds in high concentrations can cause necrosis and erosion of the apical part of the villi (groups II and III). Blood biochemical analysis of fish (group II and III) receiving medium and high concentrations of chelated compounds showed high ALT activity, which was 23,02% (p<0,05) and 45,19% (p<0,05) higher compared to control, respectively. Mineral-chelate compounds, of the studied composition, at a concentration of 0,5 g/kg positively affect the histological structure of the midgut of Clarias gariepinus. This dosage of the investigated feed additive can be recommended for the practical application of rearing Clariasgariepinus in closed water installations.

Macronutrient and micronutrient deficiencies in the fish diet can affect fish growth rate, ability to resist disease, and fillet quality. Determination of effective dose of developed feed additives consisting of chelate compounds of biogenic elements and probiotic preparation based on Bacillus subtilis. Young rainbow trout were divided into four groups consisting of 100 fish each. The control group received standard food; the experimental groups received food with chelates and probiotics in different concentrations. At the end of the experiment (30 days), the middle intestine histology and morphometric parameters were studied. The use of chelated compounds alone affected the state of the intestinal villi and the infiltration of the epithelium by lymphocytes. The addition of a probiotic had a positive effect on the migration of immune cells in the intestinal villi; however, the probiotic in high concentrations contributed to a decrease in the number and area of goblet cells. Synergistic effects of chelated compounds and probiotic preparations on the morphometric parameters of the medium intestine were observed. In the proper doses, the studied feed additives might be recommended for rainbow trout farming under industrial aquaculture conditions.

Annual fish of the genus Nothobranchius are promising models for aging research. Nothobranchius reproduces typical aspects of vertebrate aging, including hallmarks of brain aging. Meclofenoxate (MF) is a well-known compound that can enhance cognitive performance. The drug is prescribed for asthenic conditions, trauma, and vascular diseases of the brain. It is believed that MF is able to delay age-dependent changes in the human brain. However, until now, there has been no study of the MF effect on the brain transcriptome. In the present work, we performed an RNA-Seq study of brain tissues from aged Nothobranchius guentheri , which were almost lifetime administered with MF, as well as young and aged control fish. As expected, in response to MF, we revealed significant overexpression of neuron-specific genes including genes involved in synaptic activity and plasticity, neurotransmitter secretion, and neuron projection. The effect was more pronounced in female fish. In this aspect, MF alleviated age-dependent decreased expression of genes involved in neuronal activity. In both treated and untreated animals, we observed strong aging-associated overexpression of immune and inflammatory response genes. MF treatment did not prevent this effect, and moreover, some of these genes tended to be slightly upregulated under MF treatment. Additionally, we noticed upregulation of some genes associated with aging and cellular senescence, including isoforms of putative vascular cell adhesion molecule 1 (VCAM1), protein O-GlcNAcase (OGA), protein kinase C alpha type (KPCA), prolow-density lipoprotein receptor-related protein 1 (LRP1). Noteworthy, MF treatment was also associated with the elevated transcription of transposons, which are highly abundant in the N. guentheri genome. In conclusion, MF compensates for the age-dependent downregulation of neuronal activity genes, but its effect on aging brain transcriptome still cannot be considered unambiguously positive.

Fish as model objects have found wide applications in biology and fundamental medicine and allow studies of behavioral and physiological responses to various environmental factors. Representatives of the genus Nothobranchius are one of the most convenient objects for such studies. Male fish belonging to the family Nothobranchiidae are characterized by extremely diverse coloration, which constantly changes, depending on the age of the fish, environmental factors, and social hierarchical status. These fish species are characterized by a short life cycle, which allows changes in coloration, an indicator of the ontogenesis stage, to be estimated. Existing methods of fish color assessments do not allow the intensity of coloration of particular body zones to be clearly differentiated. In the present study, we suggest a method of two-factor assessment of specific fish body zones using modified methods of photofixation and image processing software. We describe the protocol of the method and the results of its application to different-aged groups of male Nothobranchius guentheri . The coloration of selected areas (i.e., red spot on the gill cover (RSGC), black border on the caudal fin (BBCF), and white border on the dorsal fin (WBDF)) differed significantly according to the size and age of the fish ( p < 0.05). The data obtained suggest that N. guentheri can be a model for studying aging by the intensity of body coloration in males.

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.