Evaluation of Piscicides for Control of Ruffe

Abstract
Ruffe Gymnocephalus cernuus, a Eurasian species, was introduced into Duluth Harbor, Minnesota, in the 1980s, probably in releases of ballast water from seagoing freighters. Ruffe is now the most abundant species in the fish community; native species, such as the yellow perch Perca flavescens, trout-perch Percopsis omiscomaycus, black bullhead Ameiurus melas, and most endemic minnows, have declined. Toxicity tests of antimycin and rotenone (registered piscicides) and the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) were conducted with ruffe and other fish species in water from several tributaries to Lake Superior. Ruffe and brown trout Salmo trutta were similar in their sensitivity to antimycin and rotenone; they were about five times more sensitive to antimycin and two times more sensitive to rotenone than yellow perch. However, ruffe were about three to six times more sensitive to TFM than either brown trout or yellow perch. The effects of control treatments for sea lamprey Petromyzon marinus on ruffe populations in the Brule and Amnicon rivers were assessed by examining the mortality of caged ruffe and other fishes in these rivers before and after scheduled treatments and by comparing pretreatment and posttreatment ruffe population estimates, based on catch per unit effort in the estuaries of each river. Ruffe mortality associated with lampricide treatment was 97% in the Brule River in 1992 and about 70% in the Amnicon River in 1994. Although significant numbers of ruffe were killed at the TFM concentrations used to control sea lampreys, a higher concentration of TFM would be needed to eradicate ruffe from a stream. Even at higher concentrations, TFM treatments should allow selective removal of ruffe from river estuaries with only limited mortality among nontarget fishes.

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