( Gymnocephalus cernuus )
DESCRIPTION: Ruffe have a body shape similar to that of perch and coloration and markings are similar to the walleye. They are generally between 15 and 25 cm in total length and their head lacks scales. Ruffe have two large dorsal fins joined together; the forward fin has spiny rays and the rear fin has soft rays; anal fin has spines. Ruffe are very slimy when handled. Ruffe possess the ability to feed in darkness, cold temperatures, and turbid conditions. They typically spend daylight hours in deeper waters and move to shallower areas to feed during the night. Ruffe are tolerant of a wide range of ecological and environmental conditions including fresh and brackish waters, lacustrine and lotic systems, from 0.25-85 m in depth, montane and submontane areas oligotrophic to eutrophic waters. Ruff exhibit a preference for slow-moving waters with soft bottoms, usually without vegetation. Tolerant of temperatures near freezing to between 30 ºC and 34 ºC, however they prefer 25-30 ºC. Prefer oxygen concentrations of 5-6 mg/l and salinity they can tolerate salinities up to 12 parts per thousand. Ruffe are able to tolerate turbidity and pollution.
PATHWAYS/HISTORY: A small and aggressive benthic fish native to Europe and Asia, the ruffe has the potential to seriously impact North American freshwater ecosystems and commercial and sport fisheries. Introduced into Lake Superior during the mid-1980's, probably in ballast water discharged by transoceanic ships (believed to have originated from the Danube basin), this species has been found to spread, reproduce, and mature rapidly.
RISKS/IMPACTS: Ruffe compete for food resources with other benthivorous fish (e.g., Coregonus species, eel, perch, smelt, and sturgeon) and appear to be strong competitors for benthos. They prey on fish eggs and are considered a significant potential threat to North American fisheries (species has already made a strong impact on populations of commercially important fish species and on the commercial fishing industry in some areas of the Laurentian Great Lakes). Decreases in populations of native species (e.g., yellow perch, emerald shiners) caught in survey trawls have occurred as populations of ruffe have increased. On the positive side, Ruffe are a food source for bullheads, northern pike, yellow perch, smallmouth bass, black crappie, burbot, cormorants, heron, kingfisher, and smew; predation on ruffe by most predators remains low, but has increased slightly.
MANAGEMENT: Control Measures for ruffe include use of an alarm pheromone to potentially exclude ruffe from particular locations (e.g., spawning areas, entrances to other water bodies); use of a sex pheromone to assist in attracting and trapping ruffe; and use of an alarm sperm antibody to assist in the disruption of the reproductive processes. Ballast water management can reduce the chance of ruffe being transported to uninfested waters. Use of chemical piscicides on the periphery of reproducing populations has potential to limit range of infestation. Prohibiting transport of ruffe for use as live bait can limit spread. Effectively monitoring commercial rearing and transport of fish species used for stocking, can help avoid accidental introduction into new bodies of water. Ruffe are most likely to be confused with species such as perch, white bass and freshwater drum. Use of lampricide TFM has been effective in eliminating up to 97% of ruffe and lamprey (Petromyzon marinus) with minimal non-target mortality.
WHAT YOU CAN DO: Thoroughly draining live wells, bilge water, and bait buckets will limit spread.
PROFILE CREDIT: Dani Crosier and Dan Malloy - IMAGE CREDIT: Steffen Zienert