Abstract
Our study aimed to investigate the effect of dietary Astragalus polysaccharide (APS) on growth performance, gut and liver health and anti-viral capability of zebrafish. Zebrafish were fed control diet and the experimental diets containing 0.01% or 0.02% APS for three weeks. Growth performance, gut health parameters such as expression of inflammatory and tight junction genes, antioxidant capability, and microbiota composition were detected after three weeks feeding. Liver health was evaluated by serum ALT and AST levels, as well as expression of genes realated to inflammation and lipid metabolism. Zebrafish were challenged by SVCV at the end of feeding. The antiviral immune response was evaluated at 4 days post SVCV infection and survival rate was calculated 14 days after challenge. The results showed that 0.01% and 0.02% APS supplementation increased weight gain and decreased the FCR of zebrafish (P < 0.05). The intestinal expression of anti-inflammatory cytokine IL-10, tight junction protein 1b, and Occludin1 was significantly up-regulated in 0.01% APS group compared with control (P < 0.05). Furthermore, 0.01% APS decreased the content of MDA and increased total antioxidant capacity in zebrafish intestine, and the relative expression of SOD, GST and Gpxa were improved. Total bacteria and the abundance of Fusobacteria and Firmicutes in the intestinal microbiota was increased in 0.01% and 0.02% APS groups compared with control (P < 0.05). Zebrafish fed 0.01% APS showed higher survival rate after SVCV challenge. Accordingly, the expression of antiviral genes in the spleen was increased at 4 days post infection. In contrast to 0.01% supplementation, 0.02% APS compromised liver health, and exerted no positive effects on antiviral immunity. In conclusion, our results indicate that dietary 0.01% APS supplementation can improve growth performance, gut health and antiviral immunity of zebrafish, while 0.02% APS compromised liver health.
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