Effects of dietary β-glucan on the growth, immune responses and resistance of sea cucumber, Apostichopus japonicus against Vibrio splendidus infection

An eight-week feeding trial was conducted to determine the effects of dietary supplementation of β-glucan on the growth, immunity and resistance of sea cucumber against Vibrio splendidus infection. A basal diet was formulated to contain 20.6% crude protein and 4.8% crude lipid. Two levels (1.25 and 2.50 g/kg) of β-glucan were added to the basal diet to replace wheat. After the feeding trial, a V. splendidus injection challenge was executed to test the effects of β-glucan on disease resistance. Enhanced growth was observed in sea cucumber fed diet supplemented with 1.25 g glucan/kg, but not in sea cucumber fed diet supplemented with 2.50 g glucan/kg. The coelomocyte phagocytosis activity of sea cucumber fed β-glucan-supplemented diets was significantly (P < 0.05) higher than those of sea cucumbers fed the basal diet. In addition, phenoloxidase activity of coelomocytes was significantly (P < 0.05) enhanced by dietary supplementation of β-glucan. Sea cucumbers fed 1.25 g/kg glucan had a significant (P < 0.05) increase in respiratory burst of coelomocytes, compared to sea cucumber fed diet containing 2.50 g β-glucan/kg; however, coelomocyte respiratory burst of sea cucumber fed 2.50 g β-glucan/kg diet was not significantly different from those of sea cucumber fed the basal diet. The challenge test showed that dietary supplementation of β-glucan at inclusion level of 1.25 g/kg conferred significant protection to sea cucumber against V. splendidus infection. However, protective effect of β-glucan supplementation at 2.50 g/kg was marginal. It is concluded that dietary β-glucan has potential for use in diet formulations of sea cucumber to limit the adverse effects of V. splendidus, however, dosage should be an important consideration in administration.