Relationship between copper exposure duration, tissue copper concentration, and rainbow trout growth

Abstract

Rainbow trout fry were exposed in soft water to sublethal concentrations of copper for 60 days under controlled laboratory conditions. At 20-day intervals, fish were sampled for weight, length, and whole-body copper and metallothionein concentrations. Exposures to waterborne copper concentrations as low as 4.6 μg 1 −1 resulted in significantly reduced growth and significantly elevated whole-body copper concentrations after 20 days. Whole-body metallothionein concentrations did not differ significantly from controls. Fish did not recover or return to control growth rates throughout the entire exposure period; a 45% reduction in mean weight relative to controls observed on day 40 in the 9.0 μg 1 −1 Cu exposure was sustained through day 60. Whole-body accumulation rates of copper in fish exposed to 4.6 μg 1 −1 and higher levels of Cu increased significantly between 0 and 40 days and appeared to reach steady-state after 40 days. Copper accumulation was found to depend on dose and time. Trout exposed to higher copper concentrations accumulated more whole-body copper, with longer times to reach steady-state. Our data suggest that both accumulation capacity and copper depuration rates from a slowly exchangeable pool are concentraion-dependent. A linear model was developed for the relationship between exposure duration, copper accumulation, and fish weight: In (wet wt., μg) = 4.8 + 0.03 (exposure duration, days)—0.04 (whole-body copper, mg g −1 dry wt.) ( P < 0.01, R 2 = 0.94). Thus, growth reductions are predictable from tissue residues if exposure durations are known. Although exposure times may not be known for field-collected fish, residues may have utility in evaluating adverse effects on fish sampled in the wild because residues integrate exposure over time, space, and exposure route.