The Eurasian ruffe (Gymnocephalus cernuus) warrants particular attention because of its great potential for adversely affecting the multibillion-dollar Great Lakes sport fishery. The ruffe is a small but aggressive fish native to Eurasia. It was introduced into Lake Superior’s Duluth/Superior harbor area in the mid-1980s in the ballast water of an trans-oceanic ship.
Research between 1988 and 1991 showed the population of ruffe to increase from about 100,000 to more than two million. During this three-year period, the forage fish population decreased two- to three-fold, and yellow perch and walleye populations also declined dramatically. If the ruffe spreads to the other Great Lakes and inland waters of North America, its impact on the sport fishery and tourism economies could be catastrophic.
- Length: 4 to 6 inches (25 cm)
- Coloring: olive-brown to golden-brown on back, paler on the sides with yellowish white undersides
- Common Names: Eurasian ruffe, river ruffe, pope
- Found in Lakes: Huron and Superior
In Europe, the ruffe generally matures in two or three years, but it may mature in one year in warmer waters.
- It spawns between mid-April and July, depending on location, water temperature and preferred years.
- The ruffe starts reproducing at age two or three but can reproduce after the first year in warmer waters.
- An average female can produce 130,00 to 200,000 eggs per season.
A relative of the perch, the ruffe spends its days in deeper water and moves to the shallows to feed at night. To avoid predators, the ruffe prefers darkness, and uses special sensory organs called “neuromasts” to detect predators and prey. The ruffe also has a large, spiny dorsal fin likely unpalatable to predators.
Because the ruffe grows very fast, has a high reproductive capacity and adapts to a wide variety of environments, it is considered a serious threat to commercial and sport fishing. It also has the potential to seriously disrupt the delicate predator/prey balance vital to sustaining a healthy fishery.
Under state laws, it is illegal to possess a ruffe, dead or alive, in Michigan, Wisconsin, Minnesota and Ontario.