Crayfish can easily be transported out of water. Since prehistoric times men have transferred them from one pool to another but since 1850 they have crossed oceans. American species have been introduced into Europe to vary farming activities but not without problems for other species and the aquatic environment.

Crayfish are crustaceous decapods (with 5 pairs of legs) and can stay out of water for long periods without hardship This characteristic facilitates transport.
Since prehistoric times men have probably transported crayfish from one location to another. These transfers were only over short distances to provide food. During the Middle Ages it was overlords and the clergy who carried out this activity of farming crayfish in pools. In Switzerland, at this time, crustaceans were introduced into isolated lakes, Lake Brêt in Switzerland was populated with red footed crayfish which no longer exist in the basin. This species has today disappeared and other more resistant species have been introduced more recently. A very long time ago waters in the south of Scandinavia were populated with crayfish from Germany.

From the middle of the 19th century there have been many introductions of crayfish. Two native species are still present in Europe : The red clawed crayfish (Astacus astacus), the white clawed crayfish (Austrapotamobius pallipes) together with a number of species introduced from America : an American crayfish (Orconectes limosus), a species from Louisiana (Procambarus clarkii), one from the Pacific (Pacifastacus leniusculus) and a European species with spindly legs (Astucus leptodactylus).

Red clawed crayfish (Astacus astacus)

Why did these introductions take place? First of all it was an age for introductions of all sorts : from 1850 onwards many species of animal and plant were introduced from abroad. Acclimatization societies rewarded those who successfully introduced new species into France… For crayfish there has been an unwelcome phenomenon : plague! This disease started in Italy in the Po valley near Treviso, it then invaded the whole of Europe except for the British Isles and Spain. It is now known that the disease was first brought back from the Mississippi in ballast water (water taken into the hold of a boat to give it weight and enable it to navigate without a cargo). A seemingly unsignificant operation which had devastating consequences (even irreversible). These operations still take place and are cause for concern among shellfish producers on the coasts.

The pathogenic agent remained undiscovered for a long period. There was very little research on the subject and the fungus (Aphanomyces) was only identified in 1930 by which time it had spread over the whole of Europe. Restocking was a consequence of this situation. As crayfish disappeared from one place others were introduced from elsewhere to replace them. These operations had simply helped the disease to spread… hence the idea of introducing American species. In 1897 the first experiments were carried out with Orconectes virilis : this was a failure. In 1890 in Germany Van den Borne introduced Orconectes limosus into a lake in the Oder valley. This species arrived in the Cher near Saint-Florent in 1911. From these two spots this robust crayfish invaded the whole of Europe.

P.J. Laurent – Bulletin Français de Pisciculture n°344/345 – p 345-356