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

Exposure to a sublethal (150 microg/L) concentration of copper (Cu) can reduce the critical swimming speed (Ucrit) 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 Ucrit 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 Ucrit. Whole-body Cu was significantly related to reduction in Ucrit, and the relationship was surprisingly negative with the greatest reductions in Ucrit occurring in the fish with the lowest whole-body Cu concentrations. Whole-body Na+ was also significantly related to reduction in Ucrit, as the fish with the greatest whole-body Na+ experienced the smallest reduction in Ucrit. 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.