The effect of yeast polysaccharide (YSP) on the immune function of Apostichopus japonicus Selenka under salinity stress

We evaluated the effects of yeast polysaccharide (YSP) on the immune function of Apostichopus japonicus exposed to a decrease in salinity (3, 5, or 9 ppt/day). Juvenile sea cucumbers were fed artificial feed containing 0.5 % YSP. We measured phagocytic activity and lysozyme, acid phosphatase, and alkaline phosphatase activity 24 h after each decrease in salinity. When salinity was decreased by 3 ppt/day, after 24 h, the immune index were significantly enhanced by supplementation of the diet with YAP (P < 0.05). There was no obvious change in the phagocytic index of animals fed a YSP supplemented diet and exposed to a decrease of 5 ppt/day, though the other immune indices were significantly elevated relative to the starting control (30 ppt). The immune index was significantly higher in animals fed a YSP supplemented diet and exposed to a decrease of 9 ppt/day than in animals held at 30 ppt. It is concluded that the addition of YSP to the basal diet improved the immunocompetence of A. japonicas during exposure to the salinity stressors.