Crayfish plague

Crayfish plague, Aphanomyces astaci, is a water mould that infects crayfish, most notably the European Astacus which dies within a few weeks after being infected.

History
It arrived in Italy with ballast waters from a North American ship and quickly spread through Europe.

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 the United Kingdom in 1981, in Turkey in 1984 and in Ireland in 1987.

It has wiped out large populations of Astacus. Unfortunately, the Swedes tried to find a replacement crayfish in the 1950s and the 1960s and settled on the signal crayfish. The signal crayfish is, although more resistant than Astacus, a carrier of the plague, and efforts to reintroduce the original European crayfish have been quite unsuccessful because of subsequent large implantations of signal crayfish, most of them done on private initiative.

Transmission
Implantations of the signal crayfish was the reason for the spread of the disease to United Kingdom and Ireland. Transport of signal crayfish, red swamp crayfish and infected native european freshwater crayfish between waters is indeed the main cause for contamination. Transmission of the disease through items that has been in contact with contaminated water, for example a fishing tool, a canoe or a bird, is possible but unlikely and can occur only during the relatively short survival period of the spores, which is few days. The spores are also sensitive to high or low temperatures. It is still advised that local rules and regulations are observed and that the amount of water moved between different waters (in for example a boat) is minimized. It is also recommended to only use fishing bait from the same lake when fishing, alternatively freeze it to at least -10 °C for one day before use, if risk for contamination exists.

Signs of the disease
If large amounts of crayfish are visible during daylight hours, it can be a sign of infection - crayfish are normally nocturnal. The crayfish can also show signs of coordination difficulties and may for example be unable to turn around if they are turned on their back. Most often, however, the disease is not noted until large numbers of dead crayfish are found.

The signal crayfish
In Sweden the signal crayfish has also started to decline in significant numbers over the last years, and researchers now suspect that the signal crayfish may be less resistant to the plague than previously believed, possibly in combination with stress or another unknown disease. Research, however, is not yet finished.

Reintroduction
The crayfish plague disappears from an infected water system (connected lakes and rivers) in a few weeks, up to a month, after the last infected crayfish is gone. Reintroduction is then possible, as long as no infected waters is in contact with the lake.