Relative Contributions of Dietary and Waterborne Copper to Tissue Copper Burdens and Waterborne-Copper Tolerance in Rainbow Trout (Oncorhynchus mykiss)

In a 42-d study, rainbow trout (Oncorhynchus mykiss) were fed a diet containing either 13 or 684 mg Cu∙kg−1 and simultaneously exposed to waterborne-Cu concentrations of 5, 32, 55, or 106 μg∙L−1 (low-Cu diet) or 13, 38, 62, or 127 μg∙L−1 (high-Cu diet). There were no significant effects on mortality, growth, condition factor, or food conversion efficiency. Elevated dietary Cu increased Cu concentrations in liver (p < 0.001), kidney (p < 0.001), gill (p = 0.005), and digesta (p < 0.001). Increasing waterborne-Cu concentrations elevated Cu concentrations in liver (p = 0.018) and kidney (p = 0.002) but not in gill (p = 0.930) or digesta (p = 0.519). Waterborne-Cu exposure increased Zn concentrations in liver (p = 0.025) but decreased those in kidney (p = 0.045). For fish on the high-Cu diet, diet provided 99, 85, and 63% of the Cu in the liver for the 38, 62, and 127 μg∙L−1 waterborne-Cu treatments, respectively. Based on Cu tolerance (incipient lethal level for Cu), dietary and waterborne Cu partitioned into functionally different compartments. Although both waterborne-Cu (p < 0.00001) and dietary-Cu (p = 0.019) preexposure increased Cu tolerance, waterborne Cu had a much greater impact.