Effects of dietary Astragalus polysaccharides (APS) on survival, growth performance, activities of digestive enzyme, antioxidant responses and intestinal development of large yellow croaker (Larimichthys crocea) larvae

A 30-day feeding trial was conducted to investigate the effects of dietary Astragalus polysaccharides (APS) on survival, growth performance, activities of digestive enzyme, antioxidant responses and intestinal development of large yellow croaker (Larimichthys crocea) larvae. Five isonitrogenous (53% crude protein) and isolipidic (18% crude lipid) diets were formulated with graded levels of APS (0.00%, 0.05%, 0.10%, 0.15% and 0.20%). Results showed that larvae fed diets with 0.10% and 0.15% APS had significantly higher specific growth rate and body crude protein content. Meanwhile, larvae fed diets with 0.10% and 0.20% APS had significantly higher trypsin activity in intestinal segments (IS) at 45 days after hatch (DAH). Supplementation with 0.10% APS significantly improved the activity of alkaline phosphatase both in brush border membrane and IS of larvae at 45 DAH. Similarly, larvae fed the diet with 0.10% APS had significantly higher activity of leucine aminopeptidase in IS at 45 DAH than the control group. Also, larvae fed the diet with 0.10% APS showed significantly higher activity of superoxide dismutase in IS than the control group. Total antioxidant capacity in pancreatic segments (PS) were significantly higher in larvae fed diets with 0.15% and 0.20% than the control group. Malondialdehyde contents in PS were significantly lower in larvae fed the diet with 0.10% APS than the control group. Furthermore, supplementation of 0.10% APS significantly increased the length of intestinal microvillus and the height of enterocyte. The selected markers for intestinal epithelial proliferation and differentiation were higher expressed in larvae fed diets with APS than the control group, such as tight junction protein-2, proliferating cell nuclear antigen and sucrase-isomaltase. In conclusion, appropriate supplementation of APS (0.05% - 0.10%) could promote growth performance of large yellow croaker larvae through increasing the activities of digestive enzyme and antioxidant enzyme, improving intestinal morphology and promoting the intestinal development.