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River lamprey

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Scientific name: Lampetra fluviatilis
The river lamprey is a primitive, jawless fish, with a round, sucker-mouth which it uses to attach to other fish to feed from them. Adults live in the sea and return to freshwater to spawn.

Top facts

Stats

Length: up to 50cm
Weight: up to 150g
Average Lifespan: 4-8 years

Conservation status

Priority Species under the UK Post-2010 Biodiversity Framework.

When to see

January to December

About

One of the most primitive vertebrates still alive today, the river lamprey is a small, eel-like fish with a toothed, sucker-mouth. It uses this sucker to attach to other fish, rasping away at the flesh and feeding on bodily fluids. It also feeds on carrion. Adult river lampreys live in the sea and return to freshwater to spawn. When they find a suitable breeding place, the male will attach to the female using his sucker and wrap his body around hers, ensuring he fertilises the eggs as she lays them. Females can lay up to 25,000 eggs with a succession of males attached to her. After spawning the adults die; the young hatch, but spend several years buried in the silt. When they finally reach adult stage they will migrate out to sea.

What to look for

The river lamprey is bluish-grey on the back and sides, and white underneath. It can be distinguished from other lamprey by its two separate dorsal fins and the small number of teeth around its sucker.

Where to find

Widespread, but rare.

Did you know?

River lampreys are cartilaginous fishes (like sharks and rays), so have a skeleton of cartilage instead of bone.