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.
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
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.