Montana Field Guide

The ruffe or Eurasian 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.

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 have larger mouths.

Not known to actively migrate for spawning. Within the Great Lakes, the ruffe has spread (migrated/invaded) throughout all lakes, but this spread may have been augmented by intra-lake shipping transport (Ruffe Task Force 1992).

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.

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.

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.

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).

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).

Contact information for Aquatic Invasive Species personnel:
Montana Fish, Wildlife, and Parks Aquatic Invasive Species staff
Montana Department of Natural Resources and Conservation's Aquatic Invasive Species Grant Program
Montana Invasive Species Council (MISC)
Upper Columbia Conservation Commission (UC3)

The Ruffe exhibits rapid growth and high reproductive output, and can adapt to a wide range of habitat types (McLean 1993); therefore the species may pose a threat to native or non-native game-fish in North America.

There seems to be no limiting factors in the establishment of this species into Montana's waterbodies. It can withstand cold water temperatures that are found in Lake Superior, Northern Minnesota and would likely survive conditions during a Montana winter.