Growth and energy storage in juvenile fathead minnows exposed to metal mine waste water in simulated winter and summer conditions

Juvenile fathead minnows (Pimephales promelas) were exposed from 10 to 100 days post-hatch (dph) to metal mining effluent under simulated summer (20 °C and 16/8 light/dark) or winter (4 °C and 8/16 light/dark) conditions in order to test the winter stress syndrome hypothesis. The condition factor of fish at 100 dph was similar between seasons, and was greater in the summer effluent exposure group compared to the summer control. Whole body triglycerides were lower in the effluent exposure group compared to control under winter conditions, but not summer. Whole body burdens of several trace metals, notably Cu, Rb and Se, were greater in the effluent exposed fish at 100 dph and displayed seasonal differences in bioaccumulation. Fathead minnows were also exposed from 10 to 100 dph to graded concentrations of ammonia (0.02–0.40 mg unionized NH3/L) under summer conditions in order to investigate potential effects of this component of the effluent. There was no effect of ammonia exposure on growth parameters, but an increase in whole body triglycerides was observed at the highest exposure. The seasonal differences in bioaccumulation and biological responses suggest that winter conditions may be an important modifying factor in aquatic toxicological studies.