Interactive effect of copper and nickel on juveniles of tambaqui (Colossoma macropomum) exposed to pH 4 and pH 7

Copper (Cu) and nickel (Ni) are common in natural waters and can be toxic to fish, including those in the Amazon. The objective of this study is to assess the impact of copper (Cu) and nickel (Ni) on the biochemical and physiological characteristics of juvenile Colossoma macropomum. The study exposed 64 animals to varying concentrations of Cu and Ni, as well as a mixture of both metals, at pH levels of 4 and 7 for 96 h. The results demonstrated that pH levels significantly impacted several biological markers, including hemoglobin, catalase, lipoperoxidation (LPO), superoxide dismutase (SOD), and acetylcholinesterase (AChE). In particular, pH 7 was found to increase LPO and catalase levels while decreasing SOD and AChE levels. Notably, the study identified an inverse relationship between LPO levels and AChE activities. Exposure to Cu and Cu+Ni mix resulted in the inhibition of H⁺-ATPase activity at pH 4. At pH 4, Cu and Cu+Ni mix also inhibited Na⁺/K⁺-ATPase activity, while at pH 7, Ni and Cu+Ni mix inhibited it. The antagonistic effect of Ni and Cu on Na⁺/K⁺-ATPase was confirmed in animals exposed to a Cu+Ni mix. In all experimental conditions, superoxide dismutase (SOD) activities exhibited an increase at pH 4, which was followed by a decrease in lipid peroxidation (LPO). The effects of metals on SOD, LPO, and ACHE were found to be offset by changes in water pH.