Effects of salinity stress on osmotic pressure, free amino acids, and immune-associated parameters of the juvenile Chinese mitten crab, Eriocheir sinensis

Abstract

In this study, juvenile Chinese mitten crabs, Eriocheir sinensis, were exposed to different salinity (0, 8‰, 16‰ and 32‰) for 48 h to detect osmotic regulation and immune-related indicators. The highest survival rate of E.sinensis juveniles appeared in the 8‰ and then became significantly lower in 0, 16‰ and 32‰ salinity groups. At 8‰ salinity, Na+, Cl−, K+ and Ca2+ concentrations and Na+/K+-ATPase activity decreased as the salinity increased, meanwhile, they elevated gradually when the salinity was greater than 16‰; the values were lowest in the 8‰ group. What's more, the relative expression of transient receptor potential (TRP) channels has the same changing trend with Ca2+ concentrations. Interestingly, alanine, proline, glutamate, arginine, glycine and aspartate concentrations increased significantly at 8‰ salinity and then decreased. Superoxide dismutase (SOD), acid phosphatase (ACP), alkaline phosphatase (AKP) and phenoloxidase (PO) activities first decreased and then elevated with the increase in salinity and were lowest in the 8‰ group. Thus, free amino acids play a key role in the response of E. sinensis to salinity 0–8‰. About 8‰ salinity is suitable for E. sinensis juvenile. Freshwater and high-salinity water would reduce osmotic pressure regulation and immune defense functions of E. sinensis juveniles.