The Effect of Waterborne Mercury and Nickel on the ATPases and AChE Activities in the Brain of Freshwater Fish (Oreochromis niloticus) Depending on the Ca²⁺ Concentrations

In this study, freshwater fish Oreochromis niloticus were exposed to acute (3 days) and chronic (30 days) Hg²⁺ and Ni²⁺ in differing Ca²⁺ levels (15, 30 and 90 mg Ca²⁺/L). In the acute duration 30 µM Ni²⁺ and 0.3 μM Hg²⁺, in the chronic duration 10 µM Ni²⁺ and 0.03 μM Hg²⁺ were tested. At the end of the exposures, activities of ATPase (Total-ATPase, Na+/K+-ATPase and Mg²⁺-ATPase) and AChE were measured in the brain. There were changes upon Hg²⁺ and Ni²⁺ effects depending on the Ca²⁺ concentration though low dependence on Ca²⁺ exposure alone. Decreased activities were recorded after acute metal exposures even at high Ca²⁺ concentration. There were variable alterations in ATPase activities whereas AChE activity was mostly altered by Hg²⁺ exposure. ATPase and AChE activities were changed in both durations due to metal type and Ca²⁺ concentration differences. However, ATPase responses were more affected. Changes in the activities demonstrated the sensitivity of these vital enzymes towards environmental factors. Therefore, there is a potential using of these enzymes as biomarkers on the basis of multi-biomarker attitude in environmental toxicology studies.