Determination of Na,K-atpase activity and ion levels in the tissues of freshwater fish Oreochromis niloticus following exposure to salinity and metals (Cd, Cu)

Freshwater fish Oreochromis niloticus were exposed individually to different salinity (0, 2, 4, 8 ppt) concentrations alone and together with 1 µg/mL of cadmium and copper for different periods (1, 3, 7, 14 days). The aim of this study was to investigate the effects of salinity on metal toxicity by measuring the activity of Na+/K+-ATPase and ion (Na+, K+, Mg+2, Cl-) levels in the gill and intestine of O. niloticus.Results showed that enzyme activity varied depending upon salinity, tissue, metal and exposure duration. Na+/K+-ATPase activity changed in fish exposed to both metal and salinity in relation to exposure conditions and duration. In salinity alone group, the declining trend in enzyme activity was observed, whereas there was increasing trend in the metal+salt mixture group. There was no significant metal accumulation in salinity alone group, though there were some increases in the metal+salt mixture group, despite few decreases. There were also alterations in ion levels regarding exposure conditions, general trend being as decreases.