Determination of Na+-K+ATPase activities and ion levels in tissues of freshwater fish Oreochromis niloticus exposed to metals in waters with different harnesses

Freshwater fish Oreochromis niloticus were individually exposed to 1.0 µg/mL concentrations of Cu2+ and Cd2+ at different exposure durations in waters with different hardnesses. At the end of the exposure periods (0, 1, 7 and 14 days) Na+/K+-ATPase activities, total metal and ion levels in the gill, kidney and intestine were measured. Fish mortality was observed after Cu2+ exposure beginnig from 7th day during the experiments. Na+/K+-ATPase activity was affected mostly in the gill exposed to soft and hard water and this was followed by kidney and intestine. In addition, Cd2+ was appeared to be more effective on Na+/K+-ATPase activity than Cu2+. At the end of the experimenal protocol, total Cu2+ and Cd2+ levels accumulated significantly especially in the kidney and intestine following soft water exposures. Total ion levels also increased or decreased depending upon the hardness of water, metal species and tissue type and ordered as ion levels are Mg2+ >K+ >Na+ >Ca2+.