Effect of Acute Ammonia Stress on Antioxidant Enzymes and Digestive Enzymes in Barramundi Lates calcarifer Larvae

The acute toxicity of ammonia to barramundi Lates calcarifer larvae (15 days post-hatching, DPH) was studied with a semi-static bioassay method to understand the physical response of fish larvae to ammonia stress. In this study, 15 and 20 mg/L ammonia were tested, and 0 mg/L ammonia (control) was used as control. The activity of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), acid phosphatase (ACP), glutathione peroxidase (GSH-Px), and digestive enzymes lipase (LPS), amylase (AMS), trypsin (TRYP) were used as biochemical indicators. With the increase of residue time, the SOD activity in barramundi was elevated at 15 mg/L ammonia and decreased at 20 mg/L ammonia. CAT activity was lower at 20 mg/L ammonia. GSH-PX activity was elevated at the low ammonia concentration and decreased at the high ammonia concentration. ACP activity was elevated after exposure to ammonia. LPS and AMS activities in the control were significantly higher than those of the other groups (P<0.05). TRYP activity was elevated after exposure to ammonia. The results indicate that acute ammonia stress significantly affects antioxidant capacity and digestive capacity, and barramundi exhibited a certain tolerance of ammonia in a short time (<6h). Results from the present study will improve our understanding of the physical response of fish to ammonia and may guide hatchery practice for Lates calcarifer.