Pacifastacus leniusculus Dana, 1852 Pacifastacus leniusculus is a large, hardy The signal crayfish cool-temperate freshwater crayfish that occupies a wide range of habitats from small streams to large rivers and natural lakes, including sub-alpine lakes. It also grows well in culture ponds and is tolerant of brackish water and high temperatures. The signal crayfish is endemic to the northwestern United States and southwestern Canada, from where it was introduced into the more southerly states. It has also been introduced to Europe and Japan as part of the livefood trade and for aquaculture purposes. The signal crayfish is an aggressive competitor and has been responsiblePacifastacus for displacing nigrescens indigenous crayfish species wherever it has been introduced. The ‘Critically Endangered (CR)’ SootyP. leniusculuscrayfish ( ) native to the western USA has become extinct partly due to interspecific competition with ; the signal crayfishPacifastacus has also fortis been implicated in causing P.a reductionleniusculus in the range of the endemic ‘Critically Endangered (CR)’ Shasta crayfish ( ) (Taylor, 2002).Cambaroides Photo credit: Wikimedia Commons (User: White Knight) japonicus was introduced into Japan from Portland, Oregon, where it has reduced the range of the endemic Aphanomyces astaci on the island of Hokkaido (Kawai & Hiruta, 1999). In AustropotamobiusEurope, it has extirpated pallipes populations of the indigenous crayfish to which all non-North American crayfish are species, particularly the Vulnerable (VU) white-clawed crayfish susceptible, but to which it is relatively immune. Crayfish plague (Holdich, 1999). has caused large-scale mortalities amongst indigenous European Its main impact has been as a vector of the crayfish plague fungus, References:crayfish populations, particularly in England (Alderman, 1996). Alderman, D. J. 1996. Geographical spread of bacterial and fungal diseases of crustaceans. Reviews Science and Technology Office International Epizooitology 15: 603-632 Holdich, D. M. 1999. The negative effects of established crayfish populations. In Gherardi, F. and Holdich, D.M. (eds.) Crustacean Issues 11: Crayfish in Europe as Alien Species (How to make the best of a bad situation?) A.A. Balkema, Rotterdam, Netherlands: 31-48. Kawai, T. & Hiruta, M. 1999. Distribution of crayfish (Pacifastacus leniusculus and Cambaroides japonicus) in Lake Shikaribetsu and Shihoro, Hokkaido, Japan. Crayfish NEWS 21 (3): 1.1 Taylor, C. A. 2002. Taxonomy and conservation of native crayfish stocks, in Holdich, D. M. (Ed.), Click here to view archives of previous weeks’ species Biology of freshwater crayfish. Blackwell Science, Oxford: 236-257.