Effects of ammonia exposure on stress and immune response in juvenile turbot ( Scophthalmus maximus )

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 ), m RNA levels of HSP ( HSP 70 and 90) and formation of MDA , decreased the content of GSH and m RNA 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.