Acclimation-induced changes in the toxicity of zinc and cadmium to rainbow trout

Adults and juvenile rainbow trout exposed for 21 d to sublethal levels of zinc or cadmium exhibited significant changes in their respective incipient lethal levels (ILL). Acclimation resulted in exposure-dependent changes in both tolerance (ILL concentration) and resistance (time to ILL) in both size classes of fish for each metal. The ILLs for adult rainbow trout exposed to zinc increased from 695 μg/L at 131 h for nonacclimated fish to 2,025 μ/L at 168 h for fish previously exposed to 0.5 ILL (324 μg/L zinc). The ILLs for cadmium-exposed fish increased from 6 μg/L at 187 h for nonacclimated fish to 122 μg/L at 266 h for fish acclimated to 0.5 ILL (10.2 μg/L cadmium). Similar, although somewhat less dramatic, acclimation responses were observed for juveniles with both zinc and cadmium. Juveniles were found to be approximately three times less sensitive to the toxic effects of the metals than were adult fish.