Effect of the lampricide 3-trifluoromethyl-4-nitrophenol on the pink heelsplitter

The lampricide 3-trifluoromethyl-4-nitrophenol (TFM) is used to selectively kill sea lampreys (Petromyzon marinus ) in the tributaries of the Great Lakes. Over the years, TFM was tested most often on nontarget fishes and only occasionally on invertebrates, including freshwater mussels. We exposed pink heelsplitters (Potamilus alatus ) to TFM concentrations and exposure times similar to those in lampricide treatments. Tests were conducted in water similar in quality to the Poultney River, New York, a stream that contains pink heelsplitters and is scheduled for lampricide treatment in 1991. Mussels were exposed to TFM for either 12 or 24 h and observed daily in well water for 14 days. Ninety percent of the mussels exposed to 3.5 mg/L of TFM for 12 h survived, however, only 50% of the mussels exposed to that concentration for 24 h survived. TFM seems to narcotize or anesthetize mussels. Mortality of mussels exposed to 3.5 mg/L TFM for 12 h seemed to be 60% immediately after treatment, but the actual mortality was only 10% after a 14-day recovery period.