Effects of dietary fucoidan on growth performance, digestion, immunity, antioxidant and glucolipid metabolism of juvenile sea cucumber (Apostichopus japonicus)

Sea cucumber (Apostichopus japonicus) is an aquatic economic variety with great nutritional value, and its polysaccharide is one of the main functional substances in the body of A. japonicus, which has the function of anti-oxidation and immunity promotion. With the development of A. japonicus breeding industry, the formula feed of A. japonicus puts forward higher requirements. Fucoidan is rich in fucoses, which can regulate the immunity and lipid metabolism of animals. This study investigated the effects of dietary fucoidan on growth performances, digestion, immunity, antioxidant, and glucolipid metabolism of A. japonicus. Six isonitrogen and isoenergetic experimental diets were formulated to contain graded levels of fucoidan, namely 0.00% (D0), 0.44% (D1), 0.88% (D2), 1.41% (D3), 1.89% (D4) and 2.38% (D5) dry diets. Each diet was randomly assigned to triplicate tanks of A. japonicus with initial body weight (16.75±0.07) g for 60 days. The result shows: ①The weight gain rate of sea cucumber in D2 and D3 groups was significantly higher than that in D0 group(P<0.05). The contents of body wall crude fat and polysaccharide of A. japonicus reached the maximum in D2 and D3 groups, respectively. Lipase activity in D1 and D2 groups was significantly higher than that in other groups(P<0.05). Amylase activity in D3 group was significantly higher than that in other groups (P<0.05). ②The activities of intestinal lysozyme and superoxide dismutase reached the maximum value in D4 group; Malondialdehyde content in group D1 was significantly lower than that in other groups (P<0.05). ③ Phosphofructokinase activity in D2 group was significantly lower than that in D0 and D1 groups (P<0.05), pyruvate kinase in D3 group was significantly lower than that in other groups (P<0.05); The activity of phosphoenolpyruvate carboxykinase reached the minimum value in D2 group. The activities of fatty acid synthase and carnitine palmitoyl transferase-1 in D1 and D2 groups were significantly higher than those in other groups(P<0.05). ④The fluorescence quantitative results showed that the expression level of GDP-mannose-4, 6 dehydrase in D2 group was significantly lower than that in D0 group(P<0.05), while fucokinase, sulfotransferase, chondroitin sulfate and synthase in D2 group were significantly higher than that in D0 group(P<0.05). Conclusions: The effects of dietary fucoidan can promoted the growth of A. japonicus, improved the digestive, immune and antioxidant capacity of the body, increased the efficiency of lipid metabolism, and decreased the efficiency of glucose metabolism. It was found that the fucoidan can inhibit the de novo pathway of GDP-fucose, promote the salvage pathway, and up-regulate the synthesis pathway of chondroitin sulfate polysaccharide. With the weight gain rate as an evaluation indicator, quadratic regression analysis showed that the optimum dietary fucoidan of A. japonicus with body weight 16.75 g was 1.116% diet. This study can provide theoretical basis for the rational utilization of Fucoidan and the deposition of chondroitin sulfate polysaccharide in the diet of A. japonicus, and promoting the high-quality development of A. japonicus aquaculture.