LAUSR

The aim of this study was to investigate the effects of ammonia exposure on stress and immune response in turbot. The species was exposed to five total ammonia nitrogen (TAN) concentrations: 0 (control), 1, 5, 20 and 40 mg L−1 for 96 h. After 0, 24, 48 and 96 h of exposure, blood samples were collected to measure the levels of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH), cortisol, growth hormone (GH), lysozyme (LZM), complement 3 (C3), complement 4 (C4) and immunoglobulinM (IgM); liver samples were taken to analyse oxidative stress parameters (superoxide dismutase, SOD; catalase, CAT; glutathione, GSH; malondialdehyde, MDA), and gene expression of heat shock proteins (HSP 70 and HSP 90) and insulin-like growth factor-1 (IGF-1). The results showed that exposure to higher concentrations of TAN (20 and/or 40 mg L−1) enhanced the levels of CRH, ACTH and cortisol and attenuated the levels of GH, LZM, C3, C4 and IgM in plasma of turbot after 48 and 96 h. In liver, TAN (20 and/or 40 mg L−1) apparently increased the activities of antioxidative enzymes (SOD and CAT), mRNA levels of HSP (HSP 70 and 90) and formation of MDA, decreased the content of GSH and mRNA levels of IGF-1 after 48 and 96 h of exposure. Overall, our results suggested that high ammonia exposure caused activation of hypothalamic–pituitary–interrenal axis, inhibition of GH/IGF axis and immunity, and occurrence of oxidative stress.