Effects of schizophyllan on growth, immunity and intestinal microflora of Litopenaeus vannamei

Schizophyllan (SPG) is a type of polysaccharide with β-(1,6) branching β-(1,3)-D-glucan, extracted from the fruiting body, mycelium or fermentation broth of Schizophyllum communer. In order to study the effects of SPG feed on the cultivation of Litopenaeus vannamei, we selected 12 L. vannamei breeding ponds, and set up four groups according to the addition amounts of SPG Group C (0%), Group S1 (0.5%), Group S2 (1.0%) and Group S3 (2.0%) for a 56-day experiment, then we investigated the growth, blood clearance, immune indicators and intestinal microflora. The results show that the final body mass, average weight gain rate and specific weight gain rate of Group S2 were significantly higher than those of Group C, S1 and S3 (P<0.05). The height of inner epithelial cells in Group S2 and S3 were significantly higher than those in Group C and S1 (P<0.05). Compared with Group C, the contents of serum uric acid (UC) in Group S2 and S3 were significantly lower (P<0.05), but there was no significant difference in Group S1 (P>0.05). The activities of lysozyme (LZM), total nitric oxide synthase (TNOS), phenol oxidase (PO) and alkaline phosphatase (AKP) in serum of Group S2 and S3 were significantly higher than those in Group C (P<0.05). The activities of catalase (CAT), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) in Group S2 were significantly higher than those of Group C (P<0.05). Compared with the control group, the contents of serum malondialdehyde (MDA) in all experimental groups decreased to different extents (P>0.05). There was no significant difference in Ace, Chao1, Shannon and Simpson indexes of intestinal flora (P>0.05). At phylum level, compared with Group C, the abundance of Proteobacteria in the experimental groups added with SPG decreased, while that of Tenericutes increased. At genus level, compared with Group C, the abundances of Formosa, Pseudoruegeria, Muricauda and Rugella in Group S2 increased significantly (P<0.05), while the abundance of Vibrio decreased significantly (P<0.05). In conclusion, adding 1.0% SPG in feed can improve the growth performance, immunity and antioxidant capacity of L. vannamei, increase the proportion of beneficial bacteria and reduce the proportion of harmful bacteria in intestinal tract.