Effects of salinity changes on the osmoregulatory and stress responses in the bay scallop Argopecten irradians

Most marine mollusks exhibit osmoregulatory mechanisms to cope with hypo- or hyperosmotic stress. In the present study, we elucidated the effects of exposure to hyposmotic and hyperosmotic stress on bay scallop Argopecten irradians. The Na+, K+, and Cl- ions of bay scallop hemolymph traversed in a similar direction as that of surrounding salinity. Moreover, the gill Na+/K+-ATPase was affected by changes in salinity. We further evaluated the heat shock protein (HSP)70 mRNA expression in the digestive diverticula and glucose levels in the hemolymph of bay scallops. Sudden changes in salinity were found to affect the HSP70 mRNA expression and glucose levels. In 55% salt water (SW) at 48-72 h, HSP70 mRNA expression and glucose levels were reduced compared to the control. HSP70 mRNA was present in the cells of digestive diverticula tissue at higher levels in 120% SW at 72 h than in the control. A TUNEL assay revealed that salinity changes increased cell apoptosis. Thus, exposure to 55% SW or more for more than 24 h may threaten the survival of marine mollusks.