10 20 40 60 cm
mittakaava < 40 cm
Wilhelm von Wright: Pohjolan kalat, Lauri Urho, Petri Savola (Uudenmaan ympäristökeskus), Jouko Lehmuskallio
- Other names: Lampern
- Family: Lampreys – Petromyzonidae
- Similar species: brook lamprey, sea lamprey
- Size: Sea-going form 25–35 cm, max. 40 cm, lake form 18–28 cm.
- Appearance: The river lamprey is a member of the jawless fishes and is thus quite distinct from other fish. It has no paired fins, no lower jaw, and the mouth is surrounded by a round, sucker-like disc. Instead of a gill cover, the river lamprey has a row of 7 small breathing holes immediately behind each eye. The mouth has fewer teeth (just a single disc-like row) than in the much rarer sea lamprey. The teeth of river lamprey are sharp, those of the smaller brook lamprey being rather blunt. The different lampreys are best distinguished by their size: the brook lamprey seldom exceeds 15 cm, the river lamprey never reaches 50 cm, while all sea lampreys caught in Finland have been over 50 cm in length. A small lake form of the river lamprey that has ascended a river to spawn may be difficult to tell from a large brook lamprey except by examining the sharpness of the teeth. However, the 2–13 cm long eyeless larvae of both river and brook lampreys found in rivers and streams cannot be distinguished without the help of a microscope.
- Colouring: Colouration is another aid to separating the river lamprey and sea lamprey. The back of the river lamprey is a uniform dark grey while that of the sea lamprey is heavily mottled. River lampreys and brook lampreys differ little in colouring except that the former has dark spots on an otherwise pale belly, the brook lamprey having no such spots.
- Reproduction: Having spent 2–3 years at sea, the river lamprey ascends rivers and streams in autumn to spawn. It ceases feeding and spends the winter in the river before spawning in May-June on a gravelly bottom in flowing water. After spawning the adults die. The larvae spend the first 3-5 years of their life buried in the bottom mud, filtering out food from the flowing water. They then metamorphose into the eyed juvenile form, a phase that lasts some 6 months, during which they continue to remain hidden. They then begin their downstream migration to the sea. The lake form undergoes the same life cycle except that it migrates to a larger lake.
- Food: Attaches itself to the sides or gills of fish, using its teeth to rasp away the skin and eat the flesh beneath.
- Distribution and habitat: River lampreys are common along all Finland’s coasts and in rivers that feed into the sea. River construction work has reduced numbers, though not as badly as with other migratory fish. The strongest populations of river lamprey are currently in the rivers of the eastern Gulf of Finland and along the west coast. The lake form is found in several lakes, including Saimaa, Pyhäselkä, Höytiäinen, Päijänne, Konnevesi and Näsijärvi.
- Endangerment: Near threatened. Protected from April 1st to August 15th.