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

Abstract: 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 (20:5n −3 and 22:6n −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. [Copyright &y& Elsevier]