Dietary protein and astaxanthin levels on growth performance, hepatopancreas antioxidant capacity and immunity of giant freshwater prawn (Macrobrachium rosenbergii)

The giant freshwater prawn, Macrobrachium rosenbergii, is abundantly farmed in East China and Southeast Asia. To date, limited information exists on the relationship between protein and astaxanthin, and the antioxidation and non-specific immunity functions. This study was conducted to investigate the effects of dietary protein and astaxanthin levels on growth, hepatopancreas antioxidant capacity and non-specific immune response of prawns. Further, the interaction between protein and astaxanthin was determined. In total, 1800 juveniles were randomly allocated into nine treatments with four replicates in 36 net-cages. Nine iso-lipidic diets were formulated with three levels of astaxanthin (0, 100 and 200 mg kg(-1)) and protein (350, 380 and 410 g kg(-1)) respectively. Feeding trials lasted for 72 days. The results demonstrated that survival rate, feed coefficient, protein efficiency and body composition did not differ significantly among treatments (p > 0.05), and the weight gain and specific growth rates disposed in their protein levels in diets by 410 g kg(-1) were markedly higher than the other two levels (p < 0.05). There was no significant difference in antioxidant capacity of hepatopancreas among different levels of protein (p > 0.05). The activities of acid phosphatase, alkaline phosphatase and glutathione peroxidase in hepatopancreas decreased with upgraded content of astaxanthin in diets (P < 0.05). Overall, this study implies that dietary protein levels are the key factor impacting growth performance and feed utilization, when combined with astaxanthin in diets, an interaction effect may partially occur on antioxidant enzymatic activities. However, excessive supplementation of astaxanthin may cause negative impacts on some immune-related enzymatic activities.