The effect of malathion on the temperature selection response of the common shiner, Notropis cornutus (Mitchill)

Warm- (17 degrees C) and cold-acclimated (8 degrees C) young-of-the-year, 1-year-old, and 2-year-old common shiners, Notropis cornutus (Mitchell) were exposed for 24 hr to sublethal doses (1.0, 0.25, and 0.05 microgram/L) of malathion to determine the effect of environmental concentrations of this compound on temperature selection. All three factors studied (acclimation temperature, age, and concentration) were found to affect the temperature selection response of malathion-treated fish. Malathion produced dose-dependent decreases in selected temperature (1.9 degrees to 4.3 degrees C below controls) in 17 degrees C-acclimated fish but not in 8 degrees C-acclimated fish. Two-year-olds treated with 1.0 microgram/L displayed the greatest lowering of selected temperature, followed by two-year-olds treated with 0.25 micrgram/L. One-year-olds treated with 1.0 microgram/L showed a slight lowering, while no downward shifts in selected temperature were found for young-of-the-year. Exposure to 0.05 microgram/L had no effect on any age group. Two-year-olds acclimated to 17 degrees C and exposed to 1.0 microgram/L malathion for 24 hr were placed in clean water and allowed to recover from the pesticide. It was found that the lowered selected temperature induced by malathion returned to that of the controls in 24 hr.