Copper sulfate is widely used in aquaculture as a disinfectant to control ectoparasites, pathogenic fungi, and excessive algal growth. However, elevated concentrations of copper in aquatic environments can reduce the survival rate of cultured fish. This study investigated the effect of adding 0.1 mg/L bentonite to the water in mitigating the acute toxicity of CuSO4 derived copper in Nile tilapia (Oreochromis niloticus). According to OECD guideline No. 203, fish were exposed for 96 hours to nominal copper concentrations (0, 1, 2, 4, 6, 8, 10, 12, and 14 mg/L), with and without the presence of bentonite. Fish mortality was recorded at 24-hour intervals, and lethal concentration values (LCs) were estimated using Probit analysis Program. Results showed that LC values significantly increased in bentonite-treated groups; for instance, at the 96-hour, LC50 increased from 7.819 to 9.740 mg/L, LC10 from 4.112 to 4.962 mg/L, and LC90 from 14.867 to 19.116 mg/L. These results indicate a reduction in copper toxicity and improved fish survival in the presence of bentonite. The reason for this reduction in toxicity is probably a reduction in bioavailability through the adsorption of free copper ions from water by bentonite. Therefore, bentonite can serve as a natural, economical, and eco-friendly additive for optimizing water quality and managing heavy metal toxicity in aquaculture systems.
