Effects of dietary Astragalus polysaccharides on growth, health and resistance to Vibrio harveyi of Lates calcarifer.

It is generally accepted that Astragalus polysaccharides (APS) supplementation can makes beneficial effects to fish. However, the adverse effects of APS to fish remains poorly understood. In the present study, Asian seabass Lates calcarifer were studied to assess the influence of different doses of APS on growth, health and resistance to Vibrio harveyi. Results showed that supplemental APS with 0.10 to 0.20% significantly boosted the growth performance, the protease and lipase activities of L. calcarifer. Compared with control diet, the villus length of L. calcarifer fed with APS supplemented diets was significantly higher. L. calcarifer fed with APS supplementation diets also significantly facilitated the antioxidant capacity and immune function. Meanwhile, supplemental APS with 0.10 to 0.15% significantly promoted liver health by up-regulating the expression of anti-inflammatory cytokines and down-regulating the expression of pro-inflammatory cytokines. Furthermore, survival rate of L. calcarifer challenged with V. harveyi was higher in diets supplemented with APS compared to the control. However, 0.20% APS significantly hindered the growth performance and caused immunostimulatory fatigue in L. calcarifer compared to 0.10% APS. Taken together, the present study demonstrates that supplementation APS with 0.10% is the optimal level for promoting the growth performance, health and resistance to V. harveyi of L. calcarifer, while 0.20% APS exerts adverse effects on L. calcarifer. Our findings provide novel recommendations for the application of APS supplementation in farmed fish.