A member of the Percidae family of perch, the ruffe was introduced into North America, evidently through ballast water discharge by transoceanic ships. It has become a considerable threat to the delicate predator-prey balance necessary to maintain flourishing fisheries in North American waters, especially in the Great Lakes. It has been reported only in Lake Superior waters but is likely to exist, or spread, elsewhere.
The species found and multiplying in Lake Superior has been identified as Gymnocephalus cernuus. The native range of G. cernuus is from France to the Kolyma River in eastern Siberia, and it has been introduced to England, Scotland, and Scandinavia.
Identification
The ruffe’s body shape is very similar to that of the yellow perch, and its body markings are similar to those of the walleye. It has a spiny first dorsal fin connected to a second soft dorsal fin, two deep sharp spines on the anal fin, one sharp spine on the pelvic fins, and sharp spines on the gill cover. The dorsal fins have rows of dark spots, the eyes are large and glassy, and the mouth is small and downturned. There are no scales on its head.
Size/Age
The ruffe seldom exceeds 6 inches in length but can attain a length of 10 inches. Most female ruffe live for 7 years but may live up to 11 years. Males generally live 3 to 5 years.
Life history/Behavior
The ruffe generally matures in 2 to 3 years and spawns between mid-April and July, depending on location, temperature, and habitat. Young ruffe have a faster growth rate than many of their competitors, and adults reproduce prolifically, which allows for quick population expansion. It is a nocturnal fish, spending its days in deeper water and moving shallower to feed at night.
Food
The ruffe’s primary diet is small aquatic insects and larvae, although it may consume fish eggs.
Other Names
Eurasian ruffe; French: grémille; German: kaulbarsch; Polish: jazgarz; Russian: yersh obyknovennyi.
Habitat
The ruffe occurs in freshwater and in brackish waters with 3 to 5 parts per million salinity. It exists in a variety of lake environments, preferring turbid areas and soft bottoms without vegetation. In rivers, it prefers slower-moving water. It is more tolerant of murky and eutrophic conditions than are many other perch.
