The effects of astragalus polysaccharides on the growth, heat stress tolerance and related gene expression of the leech Whitmania pigra

Whitmania pigra is an aquatic annelid with broad pharmacological effects and is widely used for treatment of cardiovascular diseases in Asia. One of the main factors limiting its commercial production is its weak heat stress tolerance. To assess the effects of astragalus polysaccharide (APS) on the growth and heat stress tolerance of W. pigra and the underlying mechanisms, six APS concentration treatments (0‰, 0.01‰, 0.03‰, 0.05‰, 0.07‰ and 0.09‰) were formulated to explore their influence on growth, digestive enzymes and the expression of immune- and growth-related genes at 26°C or 35°C. The results showed that APS significantly enhanced the final weight, weight gain rate, specific growth rate, digestive enzyme and anti-reverse enzyme activity, and the relative expression level of growth hormone, insulin-like growth factor-1 and digestive enzyme-related genes. The 0.07‰ APS group showed significantly greater values than the other groups (p < 0.05). APS up-regulated the relative expression of HSP70 and immune-related genes under heat stress, and the 0.07‰ group showed the greatest modulatory effect. Overall, APS can promote growth, immunity and heat stress resistance in W. pigra, and the recommendation dietary APS level was 0.07‰.