A comparative evaluation of the effects of copper and nickel on the growth of the freshwater fish Cyprinus carpio and amelioration by Pistia stratiotes

Objectives: The main objectives of this research were to identify if the presence of the aquatic weed Pistia stratiotes in the medium could influence the growth of the fish Cyprinus carpio when chronically exposed to sub-lethal concentrations of Cu (0.05 and 0.1 mg/L) and Ni (0.5 and 1.0 mg/L) in the presence of the weed and to compare between effects of Cu and Ni. Methods: Experiments were conducted in cement tanks for 90 days. Accumulation of Cu and Ni in water, sediment, fish and weed was determined by Atomic Absorption Spectrophotometer at the end of the experiments. The data were taken as factors to evaluate the interaction between the treatments of metals and weed and their impact on the growth of the fish. Multiple quadratic regression models followed by surface response plots were used to evaluate the interactions and their effects on the growth of C. carpio. Results: The results indicated that the presence of the weed could reduce the accumulation of Cu and Ni in the sediment and fish and thus could ameliorate the ill effects of these metals on the growth of the fish. But there was a difference in growth response between the metals. By using the quadratic polynomial regression model and the surface response plot, it was revealed that Cu produced more deleterious effects on the growth of C. carpio than Ni. The weed interacted better with Cu than Ni, but for both the metals, the weed failed to prevent adverse effects on the growth of fish at a higher concentration of the metals used. Conclusion: The quadratic polynomial regression model followed by the surface response plot is a powerful tool to analyze the interaction between the weed and the treatments of metals and to compare the adverse effects of Cu and Ni on the growth of C. carpio.