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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.

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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.