Everett Louis King Jr. Robert P. Rye Jr. 1976 We conducted laboratory static bioassays to determine acute toxicity of two lampricides -- a 70% 2-aminoethanol salt of 5,2'dichloro-4'-nitrosalicylanilide (Bayer 73) and a mixture containing 98% 3-trifluoromethyl-4-nitrophenol (TFM) and 2% Bayer 73 (TFM-2B) -- to 21 freshwater invertebrates. LC50 values were determined for 24-h exposure periods at 12.8 C. Organisms relatively sensitive to Bayer 73 were a turbellarian (<i>Dugesia tigrina</i>), aquatic earthworms (<i>Tubifex tubifex</i> and <i>Lumbriculus inconstans</i>), snails (Physa sp.) and (<i>Pleurocera sp.</i>), a clam (<i>Eliptio dilatatus</i>), blackflies (<i>Simulium sp.</i>), leeches (<i>Erpobdellidae</i>), and a daphnid (<i>Daphnia pulex</i>). The invertebrates most sensitive to TFM-2B were turbellarians, aquatic earthworms (<i>Tubifex</i>), snails (<i>Physa</i>), blackflies, leeches, and burrowing mayflies (<i>Hexagenia sp.</i>). Bayer 73 was generally much more toxic to the test organisms than TFM-2B. At lampricidal concentrations, TFM-2B was more highly selective than Bayer 73 against larval sea lampreys (<i>Petromyzon marinus</i>). application/pdf 10.1577/1548-8659(1976)105<322:ATEOTL>2.0.CO;2 en Taylor & Francis Acute toxic effects of two lampricides on twenty-one freshwater invertebrates article