EFFECTS OF THE INSECT GROWTH-REGULATOR (S)-METHOPRENE ON THE EARLY-LIFE STAGES OF THE FATHEAD MINNOW PIMEPHALES-PROMELAS IN A FLOW-THROUGH LABORATORY SYSTEM

This study assessed the effect of the insect growth regulator (IGR) (S )-methoprene on fathead minnow (Pimephales promelas) early life stages . Newly spawned (less-than-or-equal-to 24 h) minnow eggs were continuo usly exposed to (S)-methoprene concentrations of 13, 23, 48, 84, and 1 60 mug/liter for 37 days in a 2-liter proportional diluter system. No significant reductions (P > 0.05) were detected at any test concentrat ion for hatchability, fry survival, or total survival when compared to controls. Significant reductions (P less-than-or-equal-to 0.05) in le ngth and weight were detected at the 2 highest mean measured test conc entrations compared to controls. The maximum acceptable toxicant conce ntration (MATC) limits, the no-observed effect concentration (NOEC), a nd the lowest observed effect concentration (LOEC), based on analyses of fry length and weight, were 48 and 84 mug/liter, respectively. The point estimate MATC value (the geometric mean of the NOEC and LOEC) wa s calculated to be 63.5 mug/liter.