TFM is a piscicide.1It is toxic to sea lamprey (P. marinus) with LC50values ranging from 1.97 to 2.11 and 2.05 to 2.21 mg/L for sac and swim-up fry, respectively, 1.6 to 2.45 mg/L for juveniles, and 1.6 to 1.63 mg/L for adults. It is also toxic to juvenile lake sturgeon (A. fulvescens) less than 100 mm in size but not to a variety of other fish species. TFM (50 μM) uncouples oxidative phosphorylation by 22 and 28% in isolated sea lamprey and rainbow trout (O. mykiss) liver, respectively.2Formulations containing TFM have been used as lampricides in the control of larval sea lamprey populations.