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Ruffe - Gymnocephalus cernua
Other Names:  Gymnocephalus cernuus

Aquatic Invasive Species

Global Rank: G5
State Rank: SNA
* (see State Rank Reason below)

Agency Status
USFWS:
USFS:
BLM:


 

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State Rank Reason (see State Rank above)
A conservation status rank is not applicable because this species is not a suitable target for conservation activities as a result of being exotic or introduced.
 
General Description
The ruffe or Eurasion ruffe is a small (up to 10 inches; 25 cm) perch-like species that looks like a cross between a sauger, walleye and a perch. It is olive-brown to golden-brown on its back with yellowish white undersides. Like all members of the perch family, they have 2 dorsal fins, but ruffe have a fused dorsal fin characterized by 12–19 hard dorsal spines followed by 11–16 soft dorsal rays. The ruffe was probably introduced into Lake Superior within the Great Lakes near Duluth, MN via ship ballast water discharged from a vessel arriving from a Eurasian port, possibly as early as 1982-1983 (Simon and Vondruska 1991; Ruffe Task Force 1992); recent genetic research has indicated that the origin of ruffe introduced to the Great Lakes was southern Europe, not the Baltic Sea.

Diagnostic Characteristics
Average length is about 5-6 inches (12 cm), total length to about 10 inches (25 cm) long. They have a fused dorsal fin characterized by 12–19 hard dorsal spines followed by 11–16 soft dorsal rays and dark spots on membranes between the rays of the fin like a suager. Sauger, walleye and perch have their spiny and soft dorsal fins separated with a gap and larger mouths.

Range Comments
Native Species Range: Northern Europe and Asia

Montana Range: Currently not known to occur in any waterbody in Montana.

Introduced Range Comments: The ruffe has been documented in the Great Lakes states.


Habitat
The species usually occurs in lakes, but is also found in large, slow rivers, ponds and canals. It is generally found on sand and gravel bottoms, but occasionally on mud (Clarke 1981). Ruffe are bottom dwelling fish that inhabit fresh and brackish waters. They appear to do well in a variety of habitat types, but abundance appears to be correlated with eutrophication and nutrient inputs.

Food Habits
Diet consists of mainly aquatic insects, but Eurasian ruffe will occasionally consume the eggs of other fish (Ogle et al. 1995, Selgeby 1998). The diet of ruffe changes throughout the course of development, becoming more benthic in nature with increasing size (Ogle et al. 2004). A well-developed sensory system allows this species to feed at night. They have a few natural predators and the ability to hunt at night further reduces the risk of predation.

Ecology
Ruffe are primarily bottom feeders on invertebrates, preferring dark environments where they can hide from predators. Ruffe rarely grow bigger than 5-6 inches, although the sharp spines on their gill covers, dorsal and anal fins make them difficult for larger fish to eat.

Reproductive Characteristics
Ruffe grow rapidly and can reproduce in their first year. In the St. Louis River, near Duluth, Minnesota, females can lay between 45,000 and 90,000 eggs a year (Simon and Vondruska 1991).

Management
Preventing the spread of this fish into Montana's waterbodies will likely be due to diligence in making sure no live fish are transported in live wells across state lines (i.e. preventing bucket biology).

References
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Citation for data on this website:
Ruffe — Gymnocephalus cernua.  Montana Field Guide.  .  Retrieved on , from