Effects of dietary Schizochytrium limacinum on the growth, immunity and digestion enzyme activity of sea cucumber Apostichopus japonicus

Abstract:

As an immuno-potentiator Schizochytrium limacinum was widely used in aquaculture, however its impact in the farming of sea cucumber Apostichopus japonicus Selenka has not been reported. The purpose of this study is to evaluate the effects of dietary S. limacinum on the growth, immunity and the digestion enzyme activities of sea cucumber A.japonicus, and therefore to determine its optimal portion in the feeding diet.In the 8-week experiment, three groups of sea cucumber(with initial average weight of 12.5±2.0g) were fed with basic diet implemented with different portions of S. limacinum: 0.5% (Group B), 1.25% (Group C), and 2.0% (Group D).The control group (A)was fed with the same basal diet only. The results showed that the specific growth rate (SGR) was significantly higher in Group C and D compared to the control group (P<0.05). Compared to the control, Groups C and D also showed significantly higher activities in terms of alkaline phosphatase (AKP),acid phosphatase(ACP), lysozyme (LZM), superoxide dismutase (SOD), phagocytic activity, and intestinal amylase (P<0.05).When fed with 1.25% S.limacinum (Group C), the sea cucumber exhibited significantly higher respiratory burst activity in coelomic fluid and higher activity of intestinal protease than the control group (P<0.05). In Group B, the activities of AKP, LZM and intestinal amylase were significantly higher than those of the control group(P<0.05). During the feeding experiment, all the treated sea cucumbers were healthy. Based on the facts above, our conclusions are: (1) Basic diet with the addition of 1.25% S. limacinum effectively enhances the growth and the immunity of sea cucumber;(2) Long-term administration of S.limacinum should be safe in sea cucumber farming.