Caldwell, C.A., G. Alvarez, K.G. Boykin. 2014. Toxicity effects of piscicide CFT Legumine (5% rotenone) on Lithobates sp. of New Mexico. New Mexico Department of Game and Fish – Share with Wildlife (#13-516-0000-00043). 19 pp.
Conservation through restoration of imperiled fishes can result in indirect benefits to amphibian populations through removal of invasive predatory species of fish. However, very limited information is available with regards to the effects of piscicidal applications to the non-target amphibians. Of particular interest in New Mexico is the federally-listed Chiricahua leopard frog (Lithobates chiricahuensis), and the Plains leopard frog (L. blairi) listed in New Mexico as a Species of Greatest Conservation Need. These two species co-occur throughout a watershed slated for native fish restoration using a piscicide. Toxicity trials using CFT Legumine (5% rotenone) were conducted on four larval stages of L. chiricahuensis and a surrogate species for L. blairi, the northern leopard frog (L. pipiens). Larvae of L. chiricahuensis exhibited greater sensitivity than the surrogate (L. pipiens) across all Gosner stages and both species exhibited decreasing sensitivity through tadpole development. The 48 h LC50 of CFT Legumine and its active ingredient (5% rotenone) was lowest (most toxic) in L. chiricahuensis at Gosner stages 21-25 (0.42 mg/L or 21.0 µg/L rotenone). In contrast, the 48 h LC50 for L. pipiens at these earliest Gosner stages was 1.30 mg/L (65.0 µg/L rotenone). In the later Gosner stages (26-30 and 31-36) of L. chiricahuensis, toxicity effects of CFT Legumine decreased to 1.03 mg/L (51.5 µg/L) and 1.30 mg/L (65.0 µg/L rotenone), respectively. In contrast, L. pipiens was less susceptible to the piscicide at the later Gosner stages (1.26-3.06 mg/L). While both species exhibited the least sensitivity after hind limbs were complete, L. chiricahuensis continued to be more sensitive to CFT Legumine (3.40 mg/L or 170 µg/L rotenone) than L. pipiens (3.86 mg/L or 193.0 µg/L rotenone). Late Gosner stage tadpoles (37-40) of both species demonstrated a delay in metamorphosis up to 90 days (total development time) when exposed for 48 hours to sublethal concentrations of CFT Legumine. Additional research is needed to evaluate the sublethal effects of the piscicide on metamorphosis in amphibians.