The Effects of Acute Exposure to Ammonia on Oxidative Stress, Hematological Parameters, Flesh Quality, and Gill Morphological Changes of the Large Yellow Croaker (Larimichthys crocea)

SIMPLE SUMMARY: The large yellow croaker is one of the most economically valuable marine fish in China. However, ammonia accumulates in its blood through the gills and causes fish poisoning. In the past years, few studies have focused on the toxic effects of acute ammonia exposure on fish, especially on the large yellow croaker. Therefore, the aim of this study was to evaluate the effects of acute ammonia exposure on the hematological parameters, hepatic oxidative stress, gill morphological changes and meat quality of the large yellow croaker. Exposure of large yellow croakers to four ammonia solutions at concentrations of 0, 2.96, 5.92, and 8.87 mg/L for 48 h revealed changes in serum composition, as well as oxidative stress, tissue damage in liver and gills, accumulation of free amino acids, and loss of nucleotides. ABSTRACT: Ammonia is considered to be the major chemical pollutant causing fish poisoning in aquaculture. This research aimed to evaluate the impact of acute ammonia exposure on the large yellow croaker’s meat quality, gill morphology, liver oxidative stress, and hematological parameters. The fish were exposed to total ammonia nitrogen concentrations of 0, 2.96, 5.92, and 8.87 mg/L for 48 h, respectively. The findings demonstrated that all ammonia-exposed fish had higher liver lactate dehydrogenase and glutamic oxalate transaminase activities. The glucose, blood urea nitrogen, and creatinine levels in 8.87 mg/L total ammonia nitrogen (TAN) were higher than other samples. The total protein, albumin, and triglyceride levels in serum decreased significantly in ammonia-exposed samples. After 48 h of ammonia exposure, superoxide dismutase activities showed a 76.1%, 118.0%, and 156.8% increase when fish were exposed to 2.96, 5.92, and 8.87 mg/L TAN, respectively. Catalase activities and glutathione contents were considerably higher (p < 0.05) in all ammonia-treated samples compared to 0 mg/L TAN. The ammonia-treated gill lamellae become thicker, shorter, and curved. Additionally, the ammonia exposure resulted in the accumulation of free amino acids and the loss of nucleotides. The inosine monophosphate and adenosine monophosphate contents in the flesh were decreased after 12 h of exposure to 2.96, 5.92, and 8.87 mg/L ammonia compared to the control group. Overall, large yellow croakers exposed to ammonia for 6 h presented not only changes in serum composition but also oxidative stress, liver and gill tissue damage and flesh quality deterioration.