Effects of xylo-oligosaccharides on growth，immunity and intestinal flora of Litopenaeus vannamei under low salinity stress

【Objective】 This study investigated the effects of xylo-oligosaccharide（XOS）on the growth performance， antioxidant capacity，immune-related gene expression and intestinal flora structure of Litopenaeus vannamei under low salinity stress conditions，and provided theoretical basis for the development of desalination culture feeds for L. vannamei. 【Method】 According to the salinity of the cultured water and XOS addition， the 450 L. vannamei were divided into seawater control group HS0（salinity 30‰+0 mg/kg XOS），low salinity control groups LS0（salinity 3‰+0 mg/kg XOS），LS250 （salinity 3‰+250 mg/kg XOS），LS500（salinity 3‰+500 mg/kg XOS）and LS1000（salinity 3‰+1000 mg/kg XOS）. Growth indexes were calculated after 8 weeks of feeding，digestive enzyme activities and antioxidant indexes were measured by kits，meanwhile，immune-related gene expression was detected by real-time fluorescence quantitative PCR. 【Result】 Compared with the HS0 group，the growth indexes，digestive enzyme activities，antioxidant capacity and the relative expression of immune-related genes of L. vannamei in the LS0 group were all decreased. Compared with the LS0 group，the weight gain rate，specific growth rate，survival rate and amylase（AMS）activity of L. vannamei in the LS500 and LS1000 groups showed significant increase trend（P<0.05，the same below），while the malondialdehyde（MDA） content showed a significant decrease trend. Lipase（LPS），trypsin（Trp），superoxide dismutase（SOD）and catalase （CAT）activities also showed an increasing trend，but the difference was not significant（P>0.05）. In LS500 and LS1000 groups，the relative expression levels of prophenoloxidase（proPO），anti-lipopolysaccharide factor（ALF），lysozyme （LZM），toll-like receptor 1（TLR1），toll-like receptor 2（TLR2）and toll-like receptor 3（TLR3）genes in LS500 and LS1000 groups were significantly higher than LS0. The intestinal flora Shannon index，Chao1 index，ACE index of LS1000 group L. vannamei were significantly higher than LS0 group， and Simpson index was significantly lower than LS0 group. At the phylum level，the relative abundance of Proteobacteria and Bacteroidetes decreased significantly， while the relative abundance of Cyanobacteria_Chloroplast，Firmicutes and Verrucomicrobia increased significantly. At the genus level，the relative abundance of Vibrio，Spongiimonas，Arcobacter and Shewanella decreased significantly， while the relative abundance of Lactobacillus and Acinetobacter increased significantly.【Conclusion】 Under low salinity stress，the addition of 500-1000 mg/kg XOS to the feed in this study significantly increased the growth rate，antioxidant performance，immune-related gene expression and improved the composition structure of intestinal flora of L. vannamei， effectively improving the culture effect of shrimp under low salitiny stress，so that XOS can be further developed and applied as a feed additive for desalination culture of L. vannamei.