| The toxicity of a particular chemical may be affected by the pre-exposure history of the organisms involved. In this study, I investigated physiological and biochemical aspects of copper toxicity in fish pre-exposed to either different salinity regimes or to a sublethal copper concentration. In the first part of this dissertation, I studied the effects of acclimation to different salinity regimes on subsequent copper exposure in a euryhaline fish (the sheepshead minnow, Cyprinodon variegatus). Sheepshead minnows were able to effectively adjust to changes in their environmental salinity, but this adjustment affected the impact of subsequent copper exposure on osmoregulation-related variables. The effect was pronounced for sheepshead minnows acclimated to hyposmotic conditions. The second part of this dissertation focused on the occurrence and the mechanisms underlying copper acclimation in a freshwater fish (the least killifish, Heterandria formosa). I was able to show the occurrence of copper acclimation on the basis of not only differences in survival, but also through differences in biomarker endpoints like sodium loss and lipid peroxidation. With respect to mechanisms underlying copper acclimation, my research showed that the acclimated fish had higher levels of metallothioneins, while a lower net rate of copper accumulation and reduced loss of catalase activity may also have contributed to the increased tolerance resulting from the pre-exposure. |
