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Crayfish disease diagnostics

Towards a Nordic standard

image of Crayfish disease diagnostics

Crayfish utilization is a long-standing Scandinavian tradition, which unfortunately has suffered a major drawback with the introduction of crayfish plague disease about a hundred years ago. In spite of intensive research many problems in management and diagnosis of this disease are not yet solved. To evaluate ongoing research and diagnostic methodology in different countries, representatives of diagnostic laboratories involved in crayfish disease diagnostics were invited to a workshop in Kuopio to discuss the problems with crayfish diseases. The workshop was held at the Kuopio unit of the Finnish Food Safety Authority Evira. Participants from Finland, Sweden, Norway, Estonia and Latvia were present, as well as the OIE expert from the reference laboratory for crayfish plague. In the programme of the first day the state of crayfish stocks, crayfish diseases and diagnostic methods used in each country were presented and discussed. During the second day diagnostic methods were discussed in detail, as well as research projects concerning crayfish diseases. The workshop has been made possible by way of a grant from the Nordic Council of Ministers.

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Crayfish plague in Norway – outbreaks and diagnosis

In Norway, crayfish plague is classified as a group A disease, and noble crayfish (Astacus astacus) is included as an endangered species in the national red list. The history of crayfish plague in Norway is short compared to Finland and Sweden. The first mass mortality of noble crayfish was observed in the river Vrangselva in Norway in 1971, close to the Swedish boarder. Crayfish plague was suspected based on the disease history and observation of oomycete hyphae in the crayfish cuticle. However, attempts to isolate the agent in pure culture failed, and the diagnosis could not be verified. The next suspected outbreak was in the Glomma watercourse in 1987. Two years later, the Halden watercourse was infected. In the latter case, the infection had most likely been transferred from the lake Stora Le, where crayfish plague had been diagnosed on the Swedish side of the lake. Both in the Glomma and the Halden watercourses, mass mortalities were observed and direct microscopy revealed typical oomycete hyphal infections in the soft crayfish cuticle. Again, the diagnosis could not be verified as all attempts to cultivate the agent failed. In 1998 mass mortality of noble crayfish was observed in the river Lysakerelva, close to Oslo city. As in the previous cases, all attempts to cultivate the agent failed. Attempts to reestablish the noble crayfish populations of the Glomma and the Halden watercourses were done in 1989 and 1995, respectively. The populations were growing reasonably well for many years. However, in 2003, the re-established population in Glomma had suddenly disappeared without leaving any traces. In 2004, cage experiments with living control crayfish were established in Glomma, and within a few months mortality was observed. Again, crayfish plague was suspected, but could not be verified.

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