Eurasian Ruffe (Gymnocephalus cernuus) were first detected in western Lake Superior in 1986. The method of introduction is thought to be ballast discharges from ocean going vessels. Since their introduction into the Great Lakes, Eurasian Ruffe have also been detected in Alpena, Michigan in Lake Huron.
Ruffe pose a threat to native fish because they mature quickly, have a high reproductive capacity, and easily adapt to new environments. Ruffe are more tolerant of poor water conditions and have several well developed sensory organs that allow them to detect vibrations given off by both predators and prey that give them an advantage over native fishes. Native fish populations – especially yellow perch, emerald and spottail shiners, trout perch, and brown bullhead – have declined in locations where Ruffe have become established.
The preferred habitat of the Eurasian Ruffe is turbid lakes with soft bottoms and little or no vegetation. They also prefer rivers with slow moving waters.