Crayfish plague ( Aphanomyces astaci) is a water mold that infects crayfish, most notably the European Astacus which dies within a few weeks of being infected. When experimentally tested, species from Australia, New Guinea and Japan were also found to be susceptible to the infection.
Morphology
Crayfish plague invades tissue with
. The hyphae develop
sporangium that release primary spores, which develop into
secondary
after encystment. The secondary zoospores have two flagella each and can repeatedly encyst before finally reaching a host, attaching and germinating.
History
Crayfish plague first arrived in Europe in
Italy in 1859, either with imported crayfish from North America,
or in ballast water discharge.
After its original introduction in Italy in 1860, it spread quickly through Europe and was discovered in
Sweden in 1907, in
Spain in 1972, in
Norway in 1971, in
Great Britain in 1981, in
Turkey in 1984 and in
Ireland in 1987.
In 1959, to bolster dwindling stocks of native crayfish, the signal crayfish was introduced to Sweden.
This species was studied and named by the German Mycologist Friedrich Schikora (1859–1932), from a type specimen in Germany in 1906.
Transmission
Transport of signal crayfish, red swamp crayfish and infected native European freshwater crayfish between waters is the main cause of contamination, though the disease can also be spread via items that have been in contact with contaminated water, such as a
fishing or footwear.
The spores are sensitive to high or low temperatures. Most authorities have local rules and regulations to minimize the movement of water between different waterbodies (in for example a boat), and recommend that crayfish used as
fishing bait should come from the same water as that being fished, or should be frozen to at least for one day before use, if there is a risk of contamination. The spores of crayfish plague disappear from an infected water system (connected lakes and rivers) within a few weeks once the last infected crayfish is removed.
Reintroduction is then possible, as long as no infected waters are in contact with the lake.
Signs
Infection with
Aphanomyces astaci is accompanied by few signs in its early stages, and the first indication of infection may be mortality.
In the later stages, the muscles of the tail may appear whitened, or brownish-red where blood cells have encapsulated the hyphae. The effects of the
in the
oomycete can include appearing in daytime (crayfish are typically nocturnal) and a lack of coordination.
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