Leukocyte composition of peripheral blood and some hematopoietic organs of pink salmon Oncorhynchus gorbuscha from the Varzuga River

The composition of leucocytes in peripheral blood, head kidney (pronephros) and spleen of European pink salmon was studied. In peripheral blood and pronephros, lymphocytes predominate among leucocytes, while in spleen immature or blast forms of cells prevail. The proportion of content of different forms of leukocytes depended on sex and structural and functional characteristics of tissues and organs. It was found for the first time that after the change of habitat from marine to freshwater there are significant changes in the blood leucogram. The detected decrease in the proportion of lymphocytes with simultaneous increase in the number of neutrophils and blast cell forms indicates a decrease in lympho- and increase in myelopoiesis. Similar changes were recorded earlier in the leukogram of young pink and chum salmon during smoltification. It is assumed that these differences are one of the mechanisms of adaptation of salmonid fish to habitat change.