Features of the ultrastructure of the mesonephros of representatives of the order Siluriformes from different climatic zones

This article discusses the ultrastructure of interstitial cells and structural units of the nephron-mesonephros in representatives of the Siluriformes order, living in the subequatorial and temperate climate zones. The object of the study was 4 species of catfish: the bottom species Silurus glanis, an inhabitant of the Rybinsk Reservoir located in the European part of Russia; the bottom species Clarias batrachus, Clarias gariepinus and the bottom-pelagic species Mystus gulio, inhabitants of the Cai River in southern Vietnam. It is shown that the ultrastructure of the interstitial cells of Siluriformes is similar to that of freshwater bony fishes of the Cypriniformes and Perciformes orders. Neutrophils of catfish, according to the structural features of secondary granules, are similar to those of Perciformes. The ultrastructure of the nephron of catfishes is similar to that of salmonids in the presence of a neck section in the proximal tubules of the nephron. The presence of a well-developed tubular reticulum in the endocytosis zone, forming loops, characterizes the type of nutrition of the studied species. The ultrastructure of the mesonephros of catfishes of the subequatorial zone differs from that of S. glanis of the temperate zone in the morphometric characteristics of leukocytes, iontransporting cells, structural units of the renal corpuscles and nephron tubules. These morphological features reflect differences in the intensity of water exchange in the body and are an adaptation to living in conditions with average annual high temperatures.