Abstract:Ammonia can easily form in intensive culture systems due to the ammonification of uneaten food and animal excretions, and usually results in detrimental health effects to teleost. The aim of this study was to provide a reference value for the safe regulation and control of ammonia in the aquaculture of turbot, Scophthalmus maximus, and obtain the corresponding biomarkers of blood physiological indexes under acute ammonia stress. The acute toxicity effects of ammonia on young turbot [average body weight (163.90±15.31) g] were studied with a 96 h half-static toxicity test. The effects of different ammonia concentrations and exposure times on plasma physiological indexes were determined. The results showed that the semi-lethal concentration (LC50) of total ammonia (TAN) and non-ionic ammonia (NH3-N) for 96 h were 39.73 mg/L and 0.64 mg/L, respectively, when the sea water temperature was (19.0±0.5)℃, pH value 7.85, salinity 29.5, and dissolved oxygen (7.8±0.2) mg/L. The plasma epinephrine (EPI), cortisol (cortisol), superoxide dismutase (SOD), reduced glutathione (GSH), alkaline phosphatase (AKP), and blood glucose (GLU) contents or activities were significantly affected by both the ammonia concentration and exposure time. Furthermore, the interaction between ammonia concentration and exposure time also significantly impacted these indexes. The response time of plasma EPI, SOD, GSH, AKP, and GLU advanced with the increasing of ammonia concentration, while EPI, cortisol, AKP, and GLU showed a trend of increasing first and then decreasing with prolonged exposure. These plasma physiological indexes can be used as biomarkers for acute ammonia toxicity. The plasma physiological responses of the high concentration toxic group were characterized by their plasma SOD and GSH rapidly increasing over the exposure period (within 12 h), and GLU rapidly increased at 4 h and decreased sharply before death. The results suggested that the death of juveniles under acute ammonia toxicity may be due to oxidative stress, physiological metabolic disorders, and impaired respiratory function.
