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), T1 (50% 96 h LC50 of ammonia and 1 ppt salinity level), T2 (50% 96 h LC50 of ammonia and 4 ppt salinity level), T3 (30% 96 h LC50 of ammonia and 1 ppt salinity level), and T4 (30% 96 h LC50 of ammonia and 4 ppt salinity level) for 96 h). Results showed significant increase for activities of superoxide dismutase (SOD), malondialdehyde (MDA), isocitrate dehydrogenase (ICDH), and malic enzyme (ME) in T1 and T2 groups compared to the control (p<0.05). As well, catalase (CAT) activity in accompany with reduced glutathione (GSH), and reduced/oxidized glutathione ratio (GSH/GSSG) showed remarkable reduction in T1 and T2groups Compared to the control (p<0.05).  In T3 and T4 groups, only MDA content showed a significant decrease compared to the control (p<0.05). There were no differences in other parameters. In summary, results of this study showed that 96h exposure to 30% LC50 of ammonia plus 4 ppt saline increase antioxidant defense in Nile tilapia.