Dietary Astragalus polysaccharides ameliorates the growth performance, antioxidant capacity and immune responses in turbot (Scophthalmus maximus L.)

Supplying immunostimulants to aquatic feed has been an effective way to enhance the health of aquatic animals and substitute for antibiotics. In the present study, the potential effects of Astragalus polysaccharides (APS) were evaluated in turbot, Scophthalmus maximus. Two levels of APS (50 and 150 mg/kg) were added to the basal diet (CON) and a 63-day growth trial (initial weight 10.13 +/- 0.04 g) was conducted. As the results showed, significant improvement on growth performance in the APS groups were observed. In addition, dietary 150 mg/kg APS significantly increased the total antioxidant capacity (T-AOC), glutathione peroxidase (GSH-PX) and lysozyme activities in liver. Meanwhile, APS diets induced the mRNA expression of toll-like receptors (TLRs) such as tlr5 alpha, tlr5 beta, tlr8 and tlr21, while reduced the expression of tlr3 and tlr22. The expression of inflammatory genes myeloid differentiation factor 88 and nuclear factor kappa b p65 and pro-inflammatory cytokines tumor necrosis factor-alpha and interleukin-1 beta were up-regulated in APS groups while the expression of anti-inflammatory cytokine transforming growth factor beta was inhibited. Taken together, the present study indicated that Astragalus polysaccharides could remarkably enhance the growth performance, antioxidant activity and maintain an active immune response in turbot.