Rotenone induces mortality of invasive Lake Trout and Rainbow Trout embryos

Objective

Nonnative fish, including Lake Trout Salvelinus namaycush and Rainbow Trout Oncorhynchus mykiss, are actively invading lakes and streams and threatening Cutthroat Trout O. clarkii and other native species in the western United States. Programs have been implemented to suppress invasive trout using netting, trapping, electrofishing, angling, or other traditional capture methods. Because these methods are costly and primarily target older, free-swimming life stages, development of new suppression methods that target embryos on spawning areas is desired to increase suppression efficacy and reduce long-term costs.

Methods

We evaluated the capability of rotenone, N-methylpyrrolidone, diethylene glycol ethyl ether, sodium chloride, calcium carbonate, and gelatin to induce mortality of Lake Trout and Rainbow Trout embryos in controlled laboratory experiments.

Result

Exposure to liquid and powdered rotenone formulations for 12 h at 4 mg/L caused 98% ± 0.7 (mean ± SE) and 99% ± 0.6 Lake Trout mortality, respectively. Exposure to liquid and powdered rotenone formulations for 12 h at 4 mg/L caused 62% ± 4.7 and 85% ± 3.2 Rainbow Trout mortality, respectively. N-methylpyrrolidone, diethylene glycol ethyl ether, sodium chloride, calcium carbonate, and gelatin exposures were not effective at increasing embryo mortality of either species.

Conclusion

Developing embryos represent a vulnerable life history stage that can be exploited by targeted applications of rotenone. Incorporating novel suppression techniques that effectively increase mortality of embryos in an integrated pest management approach may enhance effective suppression of invasive fishes.