Adaptive branchial mechanisms in the sturgeon Acipenser naccarii during acclimation to saltwater

Variations of Na +/K +-ATPase activity and fatty-acid composition in the gills of the sturgeon Acipenser naccarii subjected to progressive acclimation to full seawater (35 ppt) were determined in relation to the hypo-osmoregulatory capacity of this species in the hyperosmotic medium. Blood samples were taken and gills arches were removed at intermediate salinity levels between 0 and 35 ppt and after 20 days at constant salinity (35 ppt). Plasma osmolality and Na +/K +-ATPase activity increased significantly with growing environmental salinity. Total saturated fatty acids (SFAs) decreased, while total polyunsaturated fatty acids (PUFAs) increased significantly with increasing salinity due mainly to changes in n − 3 PUFAs (20:5 n − 3 and 22:6 n − 3). The n − 3 / n − 6 ratio increased significantly during the acclimation process. The results show a direct relationship between salinity, increased gill Na +/K +-ATPase activity and ultrastructural changes of the gill chloride cells. Changes in the fatty-acid composition in gills of A. naccarii during progressive acclimation to full seawater suggest that variations of gill fatty acids may also have a role in osmoregulatory mechanisms.