Research Article: Interaction effect of salinity and ammonia on glutathione-dependent antioxidant defense system in the liver of Nile tilapia (Oreochromis niloticus)

The present study aimed to investigate the effect of salinity and ammonia interactions on oxidative stress response in the liver of Nile tilapia (Oreochromis niloticus). Nile tilapia were exposed to different ammonia and salinity concentrations including C (control group without ammonia and salinity), T۱ (۵۰% ۹۶ h LC۵۰ of ammonia and ۱ ppt salinity level), T۲ (۵۰% ۹۶ h LC۵۰ of ammonia and ۴ ppt salinity level), T۳ (۳۰% ۹۶ h LC۵۰ of ammonia and ۱ ppt salinity level), and T۴ (۳۰% ۹۶ h LC۵۰ of ammonia and ۴ ppt salinity level) for ۹۶ h). Results showed significant increase for activities of superoxide dismutase (SOD), malondialdehyde (MDA), isocitrate dehydrogenase (ICDH), and malic enzyme (ME) in T۱ and T۲ groups compared to the control (p<۰.۰۵). As well, catalase (CAT) activity in accompany with reduced glutathione (GSH), and reduced/oxidized glutathione ratio (GSH/GSSG) showed remarkable reduction in T۱ and T۲groups Compared to the control (p<۰.۰۵).  In T۳ and T۴ groups, only MDA content showed a significant decrease compared to the control (p<۰.۰۵). There were no differences in other parameters. In summary, results of this study showed that ۹۶h exposure to ۳۰% LC۵۰ of ammonia plus ۴ ppt saline increase antioxidant defense in Nile tilapia.