This article presents data on the mesonephros histology and ultrastructure in the Atlantic salmon from the Baltic Sea and Barents Sea populations, with an emphasis on comparisons between the following ontogenetic stages: parr, smolting, adult life at sea, the adults’ return to their natal river to spawn, and spawning. The ultrastructural changes in the renal corpuscle and cells of the proximal tubules of the nephron occurred as early as the smolting stage. Such changes reflect fundamental alterations during the pre-adaptation to life in saltwater. In the Barents Sea population, the adult salmon sampled in the sea had the smallest diameters of the renal corpuscle and proximal and distal tubules, the most narrow urinary space, and the thickest basement membrane. In the group of salmon that entered the mouth of the river and spent less than 24 h in freshwater, the structural rearrangements occurred only in the distal tubules. Better development of the smooth endoplasmic reticulum and a greater abundance of mitochondria in the tubule cells were observed in the adult salmon from the Barents Sea compared to those from the Baltic Sea. Cell-immunity activation was initiated during the parr–smolt transformation. Another pronounced innate-immunity response was registered in the adults returning to the river to spawn.

This study presents new data on the microanatomy and ultrastructure of Polypterus senegalus nephrons. It was shown that the diameter and ultrastructure of renal corpuscles, a well-developed neck segment, and ultrastructure of two types of epithelial cells of the proximal tubule are ancestral signs of the modern population of P. senegalus associated with habitat conditions in the aquatic environment. The outer diameter of the tubules, the height of the epitheliocytes, the presence of two types of epithelial cells of the intermediate and distal tubules of the corresponding ultrastructure, and a large area of nephrogenic tissue are progressive features of the modern population of P. senegalus, associated with adaptation to air respiration and periodic terrestrial migrations, which were formed at the early stages of evolution of P. senegalus convergently with lungfish and amphibians.

The results of determining the concentration of erythropoietin and hemoglobin, morphometric parameters of erythroid elements of the mesonephros and peripheral blood of Polypterus senegalus have been presented. The maturation of erythrocytes in P. senegalus occurs both in the mesonephros and in peripheral blood. The place of synthesis and localization of erythropoietin is the mesonephros. The nuclear-cytoplasmic ratio two times lower compared to teleosts, the volume of cells two times higher and their specific surface area 1.5 times larger, the more pronounced ellipsoidal shape of mature erythrocytes, and the high concentration of hemoglobin indicate that erythrocytes of P. senegalus have a significant potential for gas exchange between the external and internal environment, which is more characteristic of amphibians (Amphibia). The revealed features of erythropoiesis of the mesonephros and peripheral blood of P. senegalus are markers of adaptation to air respiration and periodic terrestrial migrations. These adaptations were formed in the early stages of the evolution of lower vertebrates convergently with lungfish (Dipnoi) and amphibians.

This paper investigates the effect of temperature increase on the behaviour of Polypterus under laboratory experimental conditions. To investigate the effect of a change in temperature regime, analysis of video recordings of animal behaviour over eight hours under acclimation conditions and under a constant temperature increase is used. The temperature increase occurred at a rate of 1,125°C/hour. The movement trajectories of the animals under normal conditions and under a sudden increase in ambient temperature are described. The paper presents results on the speed and activity of the fish movements and the number of acts of air entrapment by polypterus from the water surface. The studies show that the increase in temperature leads to an increase in the variability of the animals’ movement trajectories. A steady increase in temperature leads to an increase in the speed and activity of the animals’ movements. As the temperature regime changes, there is an increase in the number of acts of air capture from the water surface. The largest jump in activity change is observed in the second and third hours of temperature increase. The obtained material can serve as a basis for the development of ideas about the behavioural adaptation of bony fishes to the increase in ambient temperature. The observed regularities in the responses to temperature changes will make it possible to improve the technology of polypterus cultivation.

The search for new markers of high productivity of sheep and the introduction of evaluation and selection methods for these indicators is an urgent direction in breeding of Russian sheep. The material for the research was the results of assessment of exterior, live weight of Romanov sheep. Genetic studies were carried out using tissue samples (ear plucking). Polymorphism of growth hormone gene in Romanov sheep was evaluated by restriction fragment length polymorphism analysis and polymerase chain reaction. Evaluation of polymorphism of growth hormone gene in the population of Romanov sheep showed the presence of three allelic variants - AA, AB and BB, with a frequency of 0.24, 0.63 and 0.14, respectively. The statistically significant difference between the indicators of live weight in animals with genotypes GHAB and GHAA, GHAB and GHBB was: at birth 210 g and 140 g (P 0.95), respectively; at weaning 350 g and 1260 g (P 0.95), respectively. The phenotypic variability of live weight was the highest at birth and at weaning and amounted to 31.732.5 % for all genotypes. Animals with genotypes GHAA and GHAB outperformed their peers with genotype GHBB in dimensions of rump width in tuber coxae, rump width in tuber trochanterica, chest width, chest circumference, and therefore, had a wide body. When studying the phenotypic and genetic correlations of measurements of exterior and live weight at the age of 12 months, a reliable positive relationship was established with height at withers height (rP = +0.13*; rG = +0.02), rump height (rP = +0.14**; rG = +0.03), rump length (rP = +0.14**; rG = +0.02). The new knowledge gained about polymorphism of GH gene and its relationship with productive traits of Romanov sheep will allow for in-depth evaluation, targeted selection and selection of individuals with desirable genotypes.

Layer-by-layer serial histological sections were used to reconstruct the mesonephros of P. senegalus. The distribution pattern of the structure of both nephron and hematopoietic tissue was shown to be similar to the general structure observed in ray-finned fishes. Most of the hematopoietic tissue of animal origin was revealed to be located at the cranial-ventral pole of the organ. The largest number of renal corpuscles, all with the smallest surface area and located the most distant from one another, was found in the caudal part of the mesonephros. Such an arrangement of the structural units of the kidney, coupled with the high vascularization level of the organ (the position of extraorganic and multiple branching intraorganic vessels), makes it possible to create a sufficiently increased pressure to determine the destination, thus bringing the P. senegalus kidney closer to the amphibian mesonephros. These features could have been evolutionarily fixed in the basal groups of ray-finned fishes and preserved in the process of evolutionary development, manifesting themselves in evolutionarily young species of this group.