ABSTRACT
Exposure to environmental pollutants or xenobiotics is often toxic to fish, reducing their ability to develop, grow, reproduce, or survive. While variation among fish species in their sensitivities to pollutant classes sometimes reflects inherent differences in biological targets, it may also reflect variation in the regulation or functionality of defensive mechanisms that mitigate the effects of pollutant exposures. This chapter focuses on general mechanisms and specific examples by which fish protect against, tolerate, or resist the effects of toxic pollutants. For example, transient exposures may induce physiological acclimations that reduce sensitivity to similar exposures within one generation, or may be passed to one (or more) generations by genomic regulatory mechanisms that affect the accessibility of genes to induction, such as methylation. While genetic adaptation or evolved tolerance refers to the reduced sensitivity displayed by some fish populations following multi-generational toxic exposures and reflects inherited (genetic) changes in the regulation or functionality of defense mechanisms or biological targets. However, physiological acclimations are often energetically costly and the evolution of tolerance to toxic pollutants is rarely sufficiently rapid to rescue most fish species. Thus, the study of toxicity defense helps us to characterize and predict more holistically the ecological impacts of pollutants.
