Dietary supplementation with glutamate enhanced antioxidant capacity, ammonia detoxification and ion regulation ability in Nile tilapia (Oreochromis niloticus) exposed to acute alkalinity stress

Saline-alkali aquaculture is an important way to improve the comprehensive utilization capacity of alkaline water and alleviate the fresh water crisis. This study investigated the effects of dietary L-glutamate (Glu) on ion regulation, ammonia detoxification and antioxidant capacity in Nile tilapia (Oreochromis niloticus) exposed to acute carbonate alkalinity stress. A total of 270 fish (6.06 ± 0.12 g) were fed three different dietary Glu supplements 0%, 1.5%, and 3.0% for 45 days. After the feeding trial, the fish were exposed to fresh water (control) or 53.57 mmol/l carbonate alkaline water for 24 h. The results showed that dietary Glu not only improved the weight gain and condition factors of tilapia but also promoted three reactions in which ammonia was converted into nontoxic substrates. After 24 h of alkalinity stress, tilapia fed a 15 g/kg Glu-supplement diet had considerably higher ion transport capacity in their gills compared to the control group (p < 0.05). Moreover, the gill structure of tilapia in the 15 g/kg Glu-supplement group was intact, while the structures in the other groups were impaired. Dietary Glu supplementation (15 g/kg) significantly increased the expression of genes related to urea and glutamine (Gln) synthesis. Additionally, the ammonia excretion capacity and antioxidant capacity were greatest in tilapia in the 15 g/kg Glu-supplement group (p < 0.05). These results indicated that in addition to promoting the growth of Nile tilapia, dietary Glu supplementation ameliorate the alkalinity tolerance of Nile tilapia and prevent oxidative damage, ionic toxicity and ammonia poisoning caused by acute carbonate alkalinity stress.