Resembling miniature lobsters, freshwater crayfish are small crustaceans dwelling in cool and clean rocky streams, brooks, ponds and lakes.

Crayfish are commonly consumed in Sweden and Finland, where special crayfish parties are arranged during their catching season in the late summer.

Read more about the traditional Finnish crayfish party here.

Of the hundreds of crayfish species occurring around the world, three are found in Finland  —  the native noble crayfish (Astacus astacus), the scarce narrow-fingered crayfish (Astacus leptodactylus) and the imported signal crayfish (Pacifastacus leniusculus).

The signal crayfish is a species of freshwater crayfish found in western North America, where they are more commonly called crawfish. Crawfish are a popular ingredient in Cajun and Creole cuisine, especially in the southern state of Louisiana, U.S.A.

Picture on right: native Finnish noble crayfish (Astacus astacus, top) and American red swamp crayfish (Procambarus clarkii, bottom).

The body of crayfish consists of the head, the thorax and the abdomen, which includes the edible tail. The body is covered by a protective, hard outer shell. The crayfish have two pairs of antennae and five pairs of legs, of which the first pair are developed into pincer-like claws, used for gathering food, burrowing and fighting.

Crayfish thrive in unpolluted waters, thus acting as monitors of water quality conditions. Their habitat must offer them suitable nooks and holes where they dwell and hide during the day. They do not leave their shelter until the nightfall.

Although being principally vegetarian, crayfish are also omnivores, even cannibals, eating anything from decaying roots and leaves to meat, including crayfish smaller than themselves. Crayfish bred in fish farms are fed with vegetables and fruits.

Crayfish are solitary animals, meeting other crayfish only during mating season. They reach maturity at the age of 4 to 6 years. The mating takes place in September through to October and the young are hatched on the following summer.

The caviar of crustaceans

Crayfish are regarded a great delicacy. In Europe, they are known to have been eaten already in the Middle Ages, when they were popular food among monks during fast days.

In many monasteries, crayfish were expressly grown for food in fish tanks. Crayfish were also eaten in courts and among the nobility throughout Europe.

The demand for crayfish grew as they became a highly fashionable delicacy in the 19th century France. From there the custom of feasting on crayfish spread to other European countries, reaching also Sweden and Finland, where crayfish stocks were particularly abundant at the time. Large amounts of crayfish were exported from Finland at the turn of the 19th and 20th centuries, about as much as 15 million individuals a year.

Even though the stocks of native crayfish have since declined due to crayfish plague, the revival and protecting of the stocks and import of signal crayfish stocks have ensured that crayfish can be enjoyed also in the future.

Picture on right: shelled crayfish tail.

Signal crayfish from North America were imported to Finnish waters in the 1990s. Compared to noble crayfish, signal crayfish reaches maturity twice as quick and produces more eggs and young. It has a harder shell than noble crayfish, and is more difficult to peel. Various blind tasting tests have indicated that there is no significant taste difference between the two species, yet many of us Finns think our native noble crayfish to have a more "sophisticated", sweeter and finer flavour.

Crayfish plague

From the 1860s on, the native stocks of European crayfish have been drastically reduced due to the crayfish plague, a disease native to North America. It first spread to the European waters probably with ballast water released from a North American ship, and later again with the implantations of North American signal crayfish (from the 1960s on).

Note: In Europe, the crayfish plague was first encountered in ca 1860 in the northern Italian river Po, from which it spread throughout Europe and Russia. The plague was discovered in France in 1875, in Germany in 1880 and in Russia in 1890, from where it spread to Finland in 1893 and from Finland to Sweden in 1907 and from there to Norway in 1971. It was also encountered in Spain (1958), Britain (1981), Ireland (1987), Greece (1982) and Turkey (1984), among many other countries. The most recent infections were most likely caused by the implantations of new stocks of North American signal crayfish.

The plague is caused by a parasitic fungus, Aphanomyces astaci. It does not much harm the signal crayfish, which are often carriers of it, but is lethal to both noble and narrow-fingered crayfish that are not resistant to it. The fungus infects the crayfish by attaching itself on its shell. It starts to grow fungal filaments, penetrating through the shell into the soft tissue below, killing the crayfish within a few weeks.

The fungus is easily spread from one crayfish to another, but also from one lake system to another. This mostly happens if infected crayfish or non-sterilized fishing equipment used in contaminated water are moved to uncontaminated waters. Currently no other preventative measure than maintaining the highest level of sanitation is known to stop the spreading of the fungus.
The crayfish plague is in no way harmful to humans.

Recent studies conducted by the University of Eastern Finland have surprisingly found certain stocks of native Finnish noble crayfish to be resistant to certain strains of crayfish plague, even though they are carriers of it. The reason for this is yet to be investigated.

Catching crayfish

Crayfish are caught alive in special crayfish pots, using baits. They can also be netted or simply picked up by hand. Since crayfish are nocturnal, they are most easily caught by night, using a light to help to locate them. Unless you are a resident in a fishing area, you are required to purchase a fishing licence in order to catch crayfish in Finland.

Preparing and eating crayfish

Crayfish are most delicious when briefly cooked in salted water seasoned with crown dill.

Like lobsters, crayfish turn bright red when cooked. They are cooled in their cooking liquid absorbing salt and dill aroma to enhance their flavour. When chilled, they are shelled and eaten with fingers, accompanied by fresh dill, freshly toasted wheat bread and butter.

Formerly, crayfish were used added to various stuffings, forcemeats and pies. Later it became a practise to cook and serve them whole, while still warm.

It was not until the end of the 19th century when crayfish were first allowed to cool in their cooking liquid before serving. This way they have time to soak up all the flavours from the stock, tasting much better than those eaten immediately after cooking, as every true crayfish connoisseur knows :-)

See a recipe for cooking crayfish here.