< 20 cm
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- Family: Lampreys – Petromyzonidae
- Similar species: river lamprey
- Size: 12–16 cm.
- Appearance: The brook 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 brook lamprey has a row of 7 small breathing holes immediately behind each eye. Adult brook lampreys can be distinguished from the otherwise similar river lamprey by their size: the brook lamprey is barely the thickness of a pencil and seldom exceeds 15 cm in length, whereas river lampreys that have left the sea to ascend rivers and streams to spawn generally measure over 25 cm. A small lake form of the river lamprey that has arrived in a spawning stream is easily confused with a large brook lamprey. The distinction is in the teeth, those of the brook lamprey being blunt, while the river lamprey’s teeth are sharp. Also, the two dorsal fins are more closely connected in the brook lamprey than the river lamprey. 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: The belly of the brook lamprey is a uniform pale colour, while that of the river lamprey is similar but has irregular dark spots.
- Reproduction: Larvae of the brook lamprey spend the first 4–6 years of their life buried in the mud of the stream, filtering out nutrients from the water. They then metamorphose directly into sexually mature adults, at which point they cease feeding. The adults remain in the stream of their birth, where they spawn on sand or gravel the following spring and after spawning die.
- Food: Larvae feed on organic detritus and plankton.
- Distribution and habitat: Brook lampreys occur in small streams throughout Finland with the exception of northernmost Lapland.
Other species from the same genus
Other species from the same family
National fishing travel site of Finland: www.fishinginfinland.fi
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