Toxic levels of dietary copper in Atlantic salmon ( Salmo salar L.) parr

Abstract

Atlantic salmon ( Salmo salar) parr were exposed for 4 weeks to dietary Cu concentrations of 5 (control), 35 and 700 mg Cu kg −1 dry feed to establish maximum tolerable levels of dietary Cu. Parr exposed to 35 and 700 mg Cu kg −1 dry feed had significantly increased ( P<0.01) intestinal cell proliferation (PCNA) and apoptosis rates, and increased metallothionein (MT) concentrations compared to controls. Those responses were associated with Cu accumulation in the intestine (3.5- and 89.2-fold increases relative to controls, respectively). In contrast to the controls, the Cu-exposed groups did not grow significantly during the exposure period ( P>0.05). There were no significant changes in gill Cu, plasma Cu or liver MT levels at any of the dietary Cu concentrations, indicating that Cu homeostasis was maintained. A significant increase in liver Cu (1.6-fold relative to controls), but no significant change in liver MT, were observed only at the highest copper concentration. Cu-exposed Atlantic salmon parr showed an onset of adaptive responses (increase of intestinal PCNA, apoptosis, and MT levels) at concentrations of 35 and 700 mg Cu kg −1 dry feed, indicating that stress responses are induced at these dietary Cu concentrations.