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Ruffe (Gymnocephalus cernuus)
Order: Perciforms Perciformes Suborder: Percoidei Family: Percidae
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Foto: Lauri Urho |
Description: The ruffe is a small, greenish-brown, spiny bottom-dwelling fish. It resembles the zander (pikeperch) and the perch, but differs from them in its body colour and joined dorsal fins. Under its spiny head, there are holes filled with mucus, and the skin, too, is covered with a thick coat of slime.
Origin and distribution: The native range of the ruffe covers northern Asia and most of Europe, excluding the Iberian Peninsula, the Apennines and Scotland. In Norway, the ruffe occurs only in fresh water in the south of the country. In Finland, the ruffe is abundant in many types of waters but not in ponds with muddy bottoms. For this reason, the ruffe is not so common as the perch. The northern limit of its range is at the Maanselkä water divide, and thus it is not found in rivers draining into the Barents Sea. In the Baltic Sea, the ruffe occurs farther from the shoreline than any other freshwater fish. It thrives in moderately eutrophicated waters, but its reproduction success is impaired when eutrophication advances.
Reproduction: The spawning period of ruffe starts soon after ice meltdown and may last until July. Ruffe mature at an age of 1−3 years and a length of 6−12 cm. Fast growing males may already mature at one year of age.
Food, growth and migrations: The growth rate of the ruffe varies considerably from one body of water to another, most likely due to the variation in available food resources and the abundance of other species feeding on the same resources. In coastal waters off Helsinki, an individual 10 cm long could be 2 years old and in southern lakes about 3−4 years old, but in the oligotrophic lakes of central Finland a ruffe might take as much as 5−8 years to attain the same size. The eyes of the ruffe are adapted to dim light, and thus the species is most active in crepuscular light or in the dark. Ruffe feed on a variety of benthic animals, fish eggs included. On the other hand, perch, pike, zander (pikeperch) and burbot all prey on ruffe.
Fishing and catches: Although ruffe are not exactly a target of fishing in Finland, many people consider their eggs and soup made of ruffe a delicacy. In the early years of the 20th century, the ruffe constituted an economically important export product in the Karelian region, when live fish were transported in winter to market all the way to St. Petersburg. Finland’s abundant ruffe resources are currently largely untapped due to the small size and difficulty of processing the fish.
Vulnerability, threats and management: Most ruffe populations are not threatened but some may suffer from extensive eutrophication.
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