ULTRASTRUCTURE OF CHLORIDE CELL OF GILL EPITHELIUM AND BODY IONIC COMPOSITION OF THE FRY OF TWO SPECIES OF PACIFIC SALMON DURING MIGRATION TO THE SEA

Pacific salmon fry were collected in 2001-2002 in the rivers of Southern Sakhalin on the way of their migration to the sea. The comparison of the data on ionic content of chum salmon fry carcass, received in 2002, with those obtained in 2001, has shown that the dispersion of ion concentration values in 2002 samples was significantly smaller than in 2001.Similar results were obtained when the mass of smolts was compared. The significant decrease of Na+ concentration in chum salmon fry during migration to the sea supports the idea on an imperative stimulus formation by means of change of Na+ concentration in migrating fish. The analysis of gill chloride cell (CC) structure in chum salmon and masu salmon fry in fresh and salty water has shown, that in fishes from fresh water CC were located mainly in primary lamellae, at the basis of secondary lamellae. As a rule, CC are large, have a large nucleus with an active chromatin and a light cytoplasm with numerous elongated mitochondria containing dense matrix. Secondary lamellae are short, 1-3 cells thick and practically contain no CC. In some fishes secondary lamellae were more numerous and longer. Some part of secondary lamellae contained large CC; in this place their width was approximately 2 times greater. As a whole, CC number in these fishes was increased. Analyzing all the material received during 2 years, with respect to CC cell structure and functions, a conclusion was drawn that freshwater fry of two salmon species, both chum salmon and masu salmon, caught at the same time and practically in the same reservoirs, could be divided into 3 groups. Masu salmon underyearlings are characterized, as a rule, by a thickened secondary lamellae epithelium, which, however contained few CC. In the chum salmon smolts, on the contrary, epithelium was thin, but contained numerous CC, which demonstrate active structure in the beginning of migration to the sea. But as they approached the sea (and migration duration increased), CC activity fell, though their number remained unchanged. It was only after fish transition to the sea, that CC activity grew again, though their number remained the same.

chloride cells, gill, structure and functions, Pacific salmon fry, catadromous migration