Effects of glutamate in low-phosphorus diets on growth performance, antioxidant enzyme activity, immune-related gene expression and resistance to Aeromonas hydrophila of juvenile mirror carp (Cyprinus carpio)

This study investigated the effects of glutamate (Glu) in low-phosphorus diets on growth performance, haematological indices, antioxidant enzyme activity, immune-related gene expression and resistance to Aeromonas hydrophila in juvenile mirror carp (Cyprinus carpio) (5.07 +/- 0.02 g). Fish were fed either graded levels of Glu (0 g/kg, 5 g/kg, 10 g/kg and 20 g/kg, named G0, G0.5, G1 and G2, respectively) in a low-phosphorus diet (15 g/kg NaH2PO4, 0.49), or a normal phosphorus diet ( 20 g/kg NaH2PO4, 0.61) without added Glu (C), for 8 weeks. At the end of the feeding trial, the fish were challenged with A. hydrophila. Compared with G0 group, 10 g/kg and 20 g/kg Glu supplementation of the low-phosphorus diet significantly improved the final weight, WGR, SGR and PER, and decreased FCR (p < .05). Glu supplementation of the low-phosphorus diet significantly enhanced the T-AOC, SOD activity and GSH content in intestine (p < .05). Glu supplementation significantly reduced MDA content in foregut and midgut and increased CAT activity in midgut and hindgut (p < .05). Regarding immune-related gene expression, Glu supplementation significantly diminished the up-regulation of intestinal TNF-alpha, IL-1 beta and IL-8 mRNA levels induced by phosphorus deficiency (p < .05). The survival rate of the G1 group was significantly higher than that of the G0 group (p < .05). In conclusion, 10 g/kg Glu supplementation in low-phosphorus diets can improve the growth performance, enhance the activity of intestinal antioxidant enzymes and strengthen the immune function of juvenile mirror carp.