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 NaH₂PO_4, 0.49), or a normal phosphorus diet ( 20 g/kg NaH₂PO_4, 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‐α, IL‐1β 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.