Relationship between expression of hepatic metallothionein and sublethal stress in channel catfish following acute exposure to copper sulphate

Abstract

Copper sulphate is frequently used as a general biocide in the aquacultural industry. The acute effects of copper sulphate on sublethal endpoints of stress and tissue damage in channel catfish have not been explored previously. Consequently, the purpose of this study was to examine the effects of a therapeutically relevant dose of copper sulphate on plasma cortisol, hepatic metallothionein (MT) expression, hepatic copper content and plasma concentrations of aspartate aminotransferase (AST). Exposure of prespawn juvenile catfish to 1.7 mg/l as copper sulphate (326±9.4 μg/l copper; 175–180 mg/l CaCO 3; pH 7.45) led to time-dependent increases in hepatic MT expression, hepatic copper content as well as plasma cortisol concentrations. Exposure to a 1 h confinement stress led to a redistribution of copper to the liver but no significant increases in hepatic MT or plasma cortisol after 23 h. Neither stress nor copper exposure caused liver damage as measured by AST. The parallel expression of hepatic MT with plasma cortisol and hepatic copper residues suggests that MT may serve as a useful indicator of acute stress and acute exposure to copper sulphate in channel catfish.