Histologic Evaluation of the Safety of Copper Sulfate to Channel Catfish

Abstract

A histological study was done to evaluate the effect of waterborne exposures of copper sulfate (CuSO₄) on channel catfish Ictalurus punctatus. Channel catfish were exposed daily for 11 consecutive days to three concentrations of CuSO₄ representing one, three, and five times the recommended therapeutic level based on the total alkalinity. Fish were treated with CuSO₄ in water flow-through tanks at a flow rate of 0.633 L/min. More than half the Cu was flushed in 1 h, which is similar to the elimination rates in ponds (due to the rapid uptake of Cu by aquatic plants or algae and the binding to organic and inorganic material). All fish were clinically normal and no fish died during the experiment. All examined tissues were grossly and histologically normal as well. The absence of histological lesions was attributed to the brief daily exposure to copper and to moderate total alkalinity and total hardness of the well water used. The results of this study suggest that CuSO₄ is safe for channel catfish provided that the treatment applied is considered in relation to the total alkalinity of the water. Our study followed a protocol developed in cooperation with the U.S. Food and Drug Administration, Center for Veterinary Medicine, and was designed to support the data package required for the approval of CuSO₄ as an aquaculture therapeutant.