Toxicity of the Piscicide Rotenone to Columbia Spotted Frog and Boreal Toad Tadpoles

The piscicide rotenone is commonly used to remove nonnative fishes from natural aquatic systems. While the effects of rotenone on fish are well documented, the effects of this chemical on amphibians are less well known. We determined the toxicity of the rotenone formulation CFT Legumine (5% rotenone) to three ages-Gosner age ranges 21-25, 30-35, and 40-45-of tadpoles of the Columbia spotted frog Rana luteiventris and the boreal toad Anaxyrus boreas under laboratory conditions. Tadpoles of both species were exposed to 0.1, 0.5, and 1.0 mg/L CFT Legumine (0.005, 0.025, and 0.050 mg/L rotenone, respectively) in static, 96-h exposure trials; surviving individuals were placed in rotenone-free water and raised until metamorphosis. In an additional experiment, Columbia spotted frog tadpoles were exposed to 1.0 mg/L CFT Legumine for 1, 2, 3, or 4 h before being placed in rotenone-free water for the duration of a 96-h exposure period. Tadpole mortality increased with increases in CFT Legumine concentration and exposure period. Individuals exposed to 1.0 mg/L of product experienced significantly greater mortality than did control tadpoles (P < 0.001), with 99-100% mortality occurring in the youngest age-group (Gosner 21-25) in both species. In Columbia spotted frog tadpoles, mortality decreased as age increased, while age did not affect mortality in boreal toad tadpoles. Rotenone produced no biologically significant effects on growth or metamorphosis. Our findings suggest that the use of 1.0 mg/L CFT Legumine to remove nonnative fish may cause significant mortality to larval amphibians if they are exposed for 96 h; exposures to lower dosages (0.5 mg/L of product) or for shorter durations (<= 4 h), however, resulted in less mortality. Fisheries managers can use these results to improve amphibian conservation in fish restoration areas and reduce the impacts on larval amphibian populations.