Investigation of antioxidant and osmoregulation systems of fish (Oreochromis niloticus) exposed to copper in differing calcium levels

Hardness values of freshwater vary depending on geographical regions. One of the most important parameters that determine water hardness is the amount of calcium (Ca+2) in the water. Metal toxicity can be affected by ions present in water. In this study, the Nile fish (Oreochromis niloticus) were exposed to different copper (Cu+2) concentrations in differing Ca+2 levels. Experiments were carried out in two different durations: acute (3 days, 0.3 μM Cu+2) and chronic (30 days, 0.03 μM Cu+2). After these durations, Na+/K+-ATPase and Mg+2-ATPase activities in the gill and small intestine and Ca+2-ATPase activity in the muscle and antioxidant enzyme activities in the liver were measured. At the end of acute and chronic experiments, there were significant (p<0.05) changes in ATPase and antioxidant enzyme activities depending on Cu+2 and Ca+2 concentrations, period and tissue type. While a decrease in ATPase activities was generally observed in fish after exposure to Ca+2+Cu+2, both increases and decreases were observed depending on Ca+2 levels alone. Although there were a few significant changes in parameters belonging to the antioxidant system in the liver after acute exposures, there were more significant changes after chronic exposures. In the chronic duration, there were increases in superoxide dismutase (SOD) and glutathione S-transferase (GST) activities, while catalase (CAT) activity decreased. On the other hand, significant increases were also observed in total glutathione (GSH) and oxidized glutathione (GSSG) levels. This study demonstrated that metal toxicity can vary in waters with different hardness values, emphasizing the need for caution in natural studies in aquatic environments. Keywords: Copper, Calcium, Oreochromis niloticus, ATPase, Antioxidant