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Sea lamprey

The sea lamprey (Petromyzon marinus) is the largest of the three lamprey species in the UK. Lamprey fossils have been found in the late Silurian and Devonian periods, approximately 450 million years ago.

Sea lamprey, copyright Paul Frear, Environment Agency

Sea lamprey are a migratory fish laying their eggs in clean, sandy gravels in rivers. The young larvae then move to the soft marginal silt of the river to grow, feeding on the algae, bacteria and detritus in the mud. When they are ready they will migrate to sea and start to feed parasitically on other fish by attaching themselves with their sucker-like mouths. They then migrate back into freshwater to spawn, after which they die. During this migration they don't feed and focus their energy on getting to suitable spawning grounds.


  • Listed on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species

  • Listed on Annex III of the Bern Convention and Annex II of the European Commission Habitats Directive (3)

  • Special Area of Conservation (SAC) Annex II species at a number of sites

  • Rare in the UK

  • Protected under the Salmon & Freshwater Fisheries Act, 1975 (as amended)

Appearance: adults are eel-like in size and shape, but they have no gill plates, paired fins or a jawed mouth. They have a mottled brownish grey colouration, which becomes an orange mottling when spawning. The mouth is a disc with numerous teeth, which it uses to attach and then rasp onto its host fish.

Typical size: 50-100cm

Lifespan: 5 to 8 years

When to see them: Juvenile sea lamprey spend their time in the mud, so you won't see them, and the adults are out at sea. However, the adults migrate back into rivers in May/June when they can be seen. After they have bred they die and people often report seeing their carcasses.


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Last Edited: 24 December 2020

photo of a location on the canals
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