Acclimation to Copper by Rainbow Trout (Salmo gairdneri) — A Modifying Factor in Toxicity

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Abstract
Lethal tolerance to copper by rainbow trout (Salmo gairdneri) increased by 60, 106, and 90% following 3-wk exposures to 0.29, 0.40, and 0.59 of the mean control incipient lethal level (ILL), 330 μg Cu/L (SD = 30; n = 25). A lower level of exposure, 0.38 ILL, represented a threshold for the onset of acclimation as tolerance was unaffected. Exposure at 0.09 ILL sensitized the trout, reducing their tolerance by 20%. The three-dimensional response surface for tolerance thus resembled a ski jump, with increases in tolerance for both duration and concentration of exposure above the threshold and sensitization below it. Because of the graded response, lethal tests on acclimated fish could be useful for rapid initial estimates of sublethal thresholds of response. Impact on growth was almost opposite to change in tolerance. Growth was reduced at 0.29, 0.40, and 0.59 ILL, enhanced at 0.18 ILL, and unaffected at 0.09 ILL. Acclimation to copper was not retained. That induced by 0.40 ILL was gradually lost during 3 wk in control water. A 4-wk exposure of fish to 0.59 ILL of copper resulted in sensitization to lethal levels of zinc. Tolerance to zinc decreased by 56%, the ILL of zinc dropping from 6.2 to 2.7 mg/L.Key words: tolerance, resistance, acclimation, copper, zinc, rainbow trout, Salmo gairdneri; toxicity
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