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Diseases of Aquatic Organisms

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DAO 97:75-83 (2011)  -  DOI:

Potent infection reservoir of crayfish plague now permanently established in Norway

Trude Vrålstad1,2,*,**, Stein I. Johnsen3,**, Rosa Ferreira Fristad1, Lennart Edsman4, David Strand1,2

1Section of Mycology, Norwegian Veterinary Institute, PO Box 750, Sentrum, 0106 Oslo, Norway
2Microbial Evolution Research Group (MERG), Department of Biology, University of Oslo, 0316 Oslo, Norway
3Norwegian Institute for Nature Research, Fakkelgården, 2624 Lillehammer, Norway
4Institute of Freshwater Research, Department of Aquatic Resources, Swedish University of Agricultural Sciences, 17893 Drottningholm, Sweden
**These authors contributed equally

ABSTRACT: Noble crayfish Astacus astacus is threatened in Europe due to invasive crayfish carrying the crayfish plague agent Aphanomyces astaci. Norway is among the last countries in which the introduction of non-indigenous crayfish has been limited through strict legislation practices. However, North American signal crayfish Pacifastacus leniusculus were recently discovered in a watercourse that has been repeatedly hit by the plague. We mapped the distribution and relative density (catch per unit effort) of signal crayfish within this lake, and performed agent-specific real-time PCR to estimate the prevalence of A. astaci in the population. The resulting length frequencies and relative density estimates clearly demonstrate a well-established signal crayfish population, in which 86.4% of the analysed individuals were confirmed carriers. The success of detection was significantly higher (84.1%) in the crayfish tailfan (i.e. uropods) than in the soft abdominal cuticle (38.4%), which is commonly used in prevalence studies. We therefore propose tailfan (uropods and telson) as the preferred tissue for studying A. astaci prevalence in signal crayfish populations. The likelihood of detecting an A. astaci-positive signal crayfish increased significantly with increasing crayfish length. Further, large female crayfish expressed significantly higher PCR-forming units values than large males. In surveys primarily exploring the presence of A. astaci-positive individuals in a population, large females should be selected for molecular analyses. Our study demonstrates that a potent crayfish plague infection reservoir, evidently originating from the illegal human introduction of signal crayfish, has permanently been established in Norway.

KEY WORDS: Alien crayfish · Signal crayfish abundance · Halden watercourse · Management ·Molecular diagnostics · Quantitative PCR

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Cite this article as: Vrålstad T, Johnsen SI, Fristad RF, Edsman L, Strand D (2011) Potent infection reservoir of crayfish plague now permanently established in Norway. Dis Aquat Org 97:75-83.

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