The physiology of copper tolerance in fathead minnows: Insight from an intraspecific, correlative analysis

Exposure to a sublethal (150 μg/L) concentration of copper (Cu) can reduce the critical swimming speed (U_crit of some fathead minnows (Pimephales promelas). The reduction is not consistent from one individual to the next, however, as some individuals experience dramatic reductions, while others maintain performance at preexposure levels. The objective of this experiment was to determine whether fish that experienced dramatic reductions in U_crit were physiologically different from more resistant individuals. Individual variation in gill Na⁺-K⁺ activated adenosine triphosphatase (ATPase) activity was not significantly associated with variation reduction in U_crit. Whole-body Cu was significantly related to reduction in U_crit, and the relationship was surprisingly negative with the greatest reductions in U_crit occurring in the fish with the lowest whole-body Cu concentrations. Whole-body Na⁺ was also significantly related to reduction in U_crit as the fish with the greatest whole-body Na⁺ experienced the smallest reduction in U_crit. Fathead minnows are differentially susceptible to sublethal concentrations of Cu; this difference appears to be related to Na⁺ ionoregulation as well as the capacity of the fish to accumulate Cu.