Effects of acute salinity stress on physiology and immunoenzymatic activity in juvenile sea cucumber, Stichopus monotuberculatus

To investigate the effects of acute salinity stress on physiology and immunoenzymatic activity in juvenile sea cucumbers, Stichopus monotuberculatus and S. monotuberculatus with body weights of 12.6 ± 3.1 g were selected as study subjects, and a salinity of 30‰ was used as the control, while salinities of 20‰, 25‰, 35‰ and 40‰ were used as acute salinity stress treatment groups. The survival rate of S. monotuberculatus was calculated, histological changes in the intestines were observed, and the activities of superoxide dismutase (SOD), catalase (CAT), and alkaline phosphatase (AKP) in the coelomic fluid, as well as Na+/K+-ATPase in the intestine, were measured and analyzed. The results showed that juvenile S. monotuberculatus could survive at salinities of 20–35‰, and could only survive for 24 h at a salinity of 40‰. Both high and low salinity stress changed the intestinal morphology of S. monotuberculatus, as epithelial cells were damaged and necrotic, vacuolated in the intestinal villi, and had unclear brush border edges. At 6 h after salinity stress, SOD and CAT activities in coelomic fluid increased or decreased rapidly and then adjusted and recovered gradually with the extension of stress time. SOD activity in the low-salinity groups was significantly higher than that in the control group, and CAT activity was significantly higher in the low-salinity groups (20‰ and 25‰) than in the high-salinity groups (35‰ and 40‰). AKP activity in the coelomic fluid was inhibited in the low-salinity groups and showed a gradual increase with increasing salinity. Na+/K+-ATPase activities in intestines showed a slow increase in the 20‰ salinity group and then dropped back to control levels. In the other salinity groups, Na+/K+-ATPase activity was higher at 6 h and 48 h after salinity stress. The results obtained from the present study indicate that salinity stress affected the survival rate and intestinal morphology of S. monotuberculatus, and S. monotuberculatus could respond to external environmental changes by regulating the activities of antioxidant enzymes, Na+/K+-ATPase, and AKP.