Adult size of the ruffe is 3 to 5 inches.
The ruffe (pronounced like “rough”) is a small bottom-dwelling fish. They rarely grow bigger than six inches long. They have olive to gold-brown backs with yellow-white undersides, resembling a yellow perch with walleye markings.
Body Shape and Fins
Ruffe have a perch-shaped body with walleye-like markings. They have a slightly downturned mouth and no scales on their heads. They have a fused dorsal fin with 11 to 19 spines and 11 to 16 soft dorsal rays. Ruffe have one spine on the pectoral fin, two spines on the anal fin, and many small spines on the gill covers. The sharp spines make them difficult for larger fishes to eat.
The larvae feed on small zooplankton while adults are primarily bottom feeders. They prefer dark environments to hide from predators. They grow rapidly and can reproduce in their first year. The spawning period extends from late April through mid-June, and females can lay between 45,000 and 90,000 eggs per year.
Origin and Spread
The ruffe is native to Northern Europe and Asia. The species was unintentionally introduced in the United States’ Great Lakes through the discharge of contaminated cargo ship ballast water. They were first discovered near the St. Louis River in 1986. They are now established in Lake Superior but have not been found in any Minnesota lakes to date.
Don't be fooled by these look-alikes
- Trout perch (native)
- Yellow perch (native)
- Walleye (native)
The ruffe (Gymnocephalus cernuus) is a prohibited invasive species, which means it is unlawful (a misdemeanor) to possess, import, purchase, transport, or introduce this species except under a permit for disposal, control, research, or education.
Threat to Minnesota Waters
Ruffe infestations cause recreational, economic and ecological damage—changing how residents and visitors use and enjoy Minnesota waters.
- May negatively effect more desirable species such as yellow perch and walleye.
- Compete with native fish for food.
- Feed on the young of native fishes like yellow perch and walleye.
What you should do
People spread ruffe primarily through the improper use and disposal of live bait.
Whether or not a lake is listed as infested, Minnesota law requires water recreationists to:
- Clean watercraft of all aquatic plants and prohibited invasive species.
- Drain all water by removing drain plugs and keeping them out during transport.
- Dispose of unwanted bait in the trash.
- Dry docks, lifts, swim rafts and other equipment for at least 21 days before placing equipment into another water body.
There is no known effective population control for ruffe in natural water bodies at this time, therefore, efforts are focused on preventative strategies.