Effects of dietary stachyose on growth, digestive physiology and glycometabolism of juvenile sea cucumber (Apostichopus japonicus)

Stachyose is a functional oligosaccharide, which is utilized by bifidobacterium and lactobacillus in the intestines, and plays an important role in the digestive physiology and antioxidant properties of the body. Juvenile sea cucumbers Apostichopus japonicus has high nutritional value and is an important breeding species in the Yellow Sea and Bohai Sea areas of China. This study investigated the effects of dietary stachyose on growth, digestive physiology and glycometabolism of juvenile sea cucumber A.japonicus. Six experimental diets were formulated to contain the graded levels of stachyose 0 (D1, control group), 0.04% (D2), 0.11% (D3), 0.15% (D4), 0.21% (D5) and 0.27% (D6) dry diets. Each diet was randomly assigned to triplicate tanks of sea cucumber juveniles with initial body weight (11.46±0.03) g for 67 days. The results showed that there were no differences in survival rate (SR) and ratio of intestine weight to body wall weight (IBR) among all groups. Both weight gain rate (WGR) and the specific growth rate (SGR) increased with increasing stachyose content until reaching peak levels at 0.15% dietary stachyose, but decreased thereafter. The WGR and SGR of D2, D3, D4and D5 groups were significantly higher than D1 group. The WGR reached maximum value of 90.88% in the D3 group. There were no significant effects on moisture, crude protein, crude fat and ash of body wall of Apostichopus japonicus. The activities of intestinal protease, lipase and superoxide dismutase were increased when dietary stachyose content increased from 0 to 0.15% and then decreased. The protease of D3 and D4 groups were significantly higher than other groups, meanwhile, the lipase of D3 group was significantly higher than other groups. The superoxide dismutase activity of D3, D4 and D5 groups were significantly higher than the control group. The content of malondialdehyde was first decreased and then increased, and reached the lowest value in D3 group. There was no significant difference among the activities of amylase, alkaline phosphatase and acid phosphatase. The height of intestinal folds in D3 and D4 groups was significantly greater than that in the control group, and inflammatory cell infiltration appeared in D6 group. There were no significant differences in the ratio of intestine weight to body wall weight and the thickness of muscularis among all group. With the increase of stachyose content, the activities of glucokinase and phosphoenolpyruvate carboxykinase increased, while the activities of fructosophosphate phosphokinase and pyruvate kinase increased first and then decreased. The glucokinase activitie of D3, D4, D5 and D6 groups were significantly higher than the control group. The fructosophosphate phosphokinase activitie of D3, D4 and D5 groups were significantly higher than the other groups, and reached maximum value in the D4 group.. The pyruvate kinase activitie of D3 groups were significantly higher than the other groups. The phosphoenolpyruvate carboxykinase activitie of D2, D3, D4 and D5 groups were significantly higher than the control group and significantly lower than D6 group. The results showed that dietary stachyose increased the glucose metabolism efficiency, improved the digestive physiology and antioxidant capacity of the body, and promoted the growth of the sea cucumber juvenile. With the weight gain rate as an evaluation indicator, quadratic regression analysis showed that the optimum dietary stachyose of sea cucumber juvenile was 0.129% diet. As a functional oligosaccharide, stachyose plays an important role in the digestion, metabolism and antioxidation of A.japonicus, and has deep research significance in the application of compound feed of A.japonicus.