Chronic toxicity study of ammonia exposure in juvenile yellow catfish Pelteobagrus fulvidraco

In aquaculture systems, long-term low ammonia stress has not received enough attention because ambient ammonia easily does not reach lethal concentrations for fish. The purpose of this study was to investigate the growth performance of yellow catfish to chronic low ammonia exposure, and to clarify the growth tolerance upper limit (GTUL) for ammonia, which can help enterprises reduce costs. We measured the 56-d survival, growth and physiological status of yellow catfish (3.96 +/- 0.05 g) reared in 0.00, 1.25, 2.50, 5.00 and 10.00 mg/L total ammonia nitrogen (TAN). The survival rate was significantly reduced at ammonia level up to 10.00 mg/L TAN. However, the weight gain rate, condition factor, feed intake, hepatosomatic index, serum acid phosphatase and immunoglobulin M contents, lysozyme activity, and Bcl2 expression were significantly decreased when ammonia level exceeded 1.25 mg/L TAN, while whole-body crude protein, muscle amino acids, serum ammonia, aspartate transaminase, liver tumor necrosis factor, interleukin 1 and 8 contents, and the expressions of GPX, TNF alpha, IL 8, P53, AKT, PTEN were significantly increased. We recommend that juvenile yellow catfish not be exposed to ammonia concentrations >1.25 mg/L TAN (0.026 mg/L NH3) for prolonged periods of time.