North American Signal Crayfish (Pacifastacus leniusulus)



North American Signal Crayfish
(Pacifastacus leniusculus)

Photo courtesy of GB Non Native Species Secretariat

To view NBN location data click here




  • Documented harmful impacts include eradication of indigenous population of white-clawed crayfish Austropotamobius pallipes through direct competition and transmission of lethal crayfish plague Aphanomyces astaci.
  • Excludes salmonids from preferred habitat
  • Impacts on other species and habitats also occur including benthic fish, aquatic invertebrates, macrophytes, and invertebrates.
  • Deliberate introduction (for wild harvest, fish food or weed control
  • Accidental introduction with stocked fish.
  • Inter-catchment spread via canals
  • Natural colonisation of tributaries from main rivers
  • Accidental or deliberate release of live crayfish intended for food in restaurants
  • Occasional movement by predators



Do not introduce into, or take crayfish from, the wild. It is illegal to be in possession of live crayfish or trap them without a licence. Licensing enquiries should be directed to: Salmon and Freshwater Fisheries, Pentland House, 47 Robb’s Loan, Tel:

If you see a crayfish in the wild, either live specimens or the remains of a dead crayfish please report it through this website (click here to make a report) and contact either:

Fisheries Research Services Freshwater Laboratory, Faskally, Pitlochry,  LB Tel: . Email

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