The ruffe (Gymnocephalus cernuus) was accidentally introduced into the Great Lakes basin from Eurasia and has established a breeding population in the St. Louis River, a major tributary to western Lake Superior. We captured young-of-the-year ruffe in the St. Louis River; acclimated groups of 90-91 fish to test temperatures of 7, 10, 15, 20, and 25 degrees C; and fed them ad libitum for 42 days at those temperatures. Ruffe grew at all five temperatures, but the optimum temperature for growth was about 21 degrees C. Because the optimum temperature for growth of walleye (Stizostedion vitreum), sauger (Stizostedion canadense), and yellow perch (Perca flavescens) is about 22 degrees C, ruffe will probably attempt to share their thermal habitat. A recent survey of the St. Louis River revealed that yellow perch and small forage fish declined sharply as ruffe abundance increased. A similar decline in yellow perch abundance in Lakes Michigan, Huron, and Erie seriously affect the fisheries in these lakes.
Additional publication details
Growth-temperature relation for young-of-the-year ruffe