IDENTIFICATION OF LAMPRICIDE FORMULATIONS AS A POTENT INDUCER OF MFO ACTIVITY IN FISH

White sucker caged in a Lake Superior tributary during a lampricide ap plication showed marked induction of hepatic mixed function oxygenase (MFO) enzymes. Laboratory trials (0.5-5.8 mg L-1, 24 h exposure) with rainbow trout confirmed that field formulations of lampricides induce MFO activity. When the two primary components of the lampricide formul ation were tested separately, MFO induction was associated with the 3- trifluoromethyl-4-nitrophenol (TFM) formulation, and not the 2, 5-dich loro-4'-nitrosalicylanilide (Bayer 73) component of the field applicat ion. Bioassays confirmed that reverse phase HPLC successfully separate d the inducing component(s) of the TFM formulation. Induction was not associated with the HPLC fraction of the formulation containing TFM, w hich was corroborated by subsequent exposures of fish to purified TFM. These biochemical effects of lampricide exposure appear to be related to the presence of an unidentified contaminant in the field formulati on. The significance of the MFO induction in terms of growth, reproduc tion, and survival is unknown, but exposure was associated with a tran sient decrease in circulating levels of steroid hormones.