Crayfish

Crayfish, crawfish, or crawdads — members of the superfamilies Astacoidea and Parastacoidea — are freshwater crustaceans resembling small lobsters, to which they are related. They breathe through feather-like gills and are found in bodies of water that do not freeze to the bottom; they are also mostly found in brooks and streams where there is fresh water running, and which have shelter against predators. Most crayfish cannot tolerate polluted water, although some species such as the invasive Procambarus clarkii are more hardy. Crayfish feed on living and dead animals and plants.^[1]

In Australia, New Zealand and South Africa, the term crayfish or cray generally refers to a saltwater spiny lobster, of the genus Jasus that is indigenous to much of southern Oceania,^[2] while the freshwater species are usually called yabby or koura, from the Indigenous Australian and Māori names for the animal respectively. An exception is the Murray Crayfish found on the Murray River.

The study of crayfish is called astacology.^[3]

Contents 1 Names 2 Anatomy 3 Geographical distribution and classification 3.1 North America 4 Fossil record 5 Crayfish plague 6 Uses 6.1 Bait 6.2 Food 6.2.1 China 6.2.2 France 6.2.3 Spain 6.2.4 Mexico 6.2.5 Scandinavia 6.2.6 United States 6.2.7 Nigeria 6.3 Pets 6.4 Production 7 References 8 Further reading 9 External links

Names

The name "crayfish" comes from the Old French word escrevisse (Modern French écrevisse) from Old Frankish *krebitja (cf. crab), from the same root as crawl. The word has been modified to "crayfish" by association with "fish" (folk etymology). The largely American variant "crawfish" is similarly derived.

Some kinds of crayfish are known locally as lobsters, crawdads,^[4] mudbugs,^[4] and yabbies. In the Eastern United States, "crayfish" is more common in the north, while "crawdad" is heard more in central and western regions, and "crawfish" further south, although there are considerable overlaps.^[5]

Anatomy

The body of a decapod crustacean, such as a crab, lobster, or prawn, is made up of nineteen body segments grouped into two main body parts, the cephalothorax and the abdomen. Each segment may possess one pair of appendages, although in various groups these may be reduced or missing. On average, crayfish grow to 17.5 centimetres (6.9 in) in length, but some grow larger.

Geographical distribution and classification

There are three families of crayfish, two in the northern hemisphere and one in the southern hemisphere. The southern-hemisphere (Gondwana-distributed) family Parastacidae lives in South America, Madagascar and Australasia, and is distinguished by the lack of the first pair of pleopods.^[6] Of the other two families, members of the Astacidae live in western Eurasia and western North America and members of the family Cambaridae live in eastern Asia and eastern North America.

Australasia has over 100 species in a dozen genera. Many of the better-known Australian crayfish are of the genus Cherax, and include the marron (Cherax tenuimanus), red-claw crayfish (Cherax quadricarinatus), yabby (Cherax destructor) and western yabby (Cherax preissii). The world's largest freshwater crayfish, Astacopsis gouldi, which can achieve a mass of up to 5 kilograms (11 lb), is found in the rivers of northern Tasmania.^[7]

Madagascar has an endemic genus, Astacoides, containing seven species.^[8]

Europe is home to seven species of crayfish in the genera Astacus and Austropotamobius.

Cambaroides is native to Japan and eastern mainland Asia.

North America

The greatest diversity of crayfish species is found in south-eastern North America, with over 330 species in nine genera, all in the family Cambaridae. A further genus of astacid crayfish is found in the Pacific Northwest and the headwaters of some rivers east of the Continental Divide. Many crayfish are also found in lowland areas where the water is abundant in calcium and oxygen rises from underground springs.^[9]

Crayfish were introduced purposely into a few Arizona reservoirs and other bodies of water decades ago, primarily as a food source for sport fish. They have since dispersed beyond those original sites.

Fossil record

Fossil records of crayfish older than 30 million years are rare, but fossilised burrows have been found from strata as old as the late Palaeozoic or early Mesozoic.^[10] The oldest records of the Parastacidae are in Australia, and are 115 million years old.^[11]

Crayfish plague

Some crayfish suffer from a disease called crayfish plague. This is caused by the water mould Aphanomyces astaci. Species of the genus Astacus are particularly susceptible to infection, allowing the more resistant signal crayfish to invade parts of Europe. Crayfish plague is not indigenous to Europe, rather it was introduced by the incorporation of new species of crayfish from the Americas.^[12]

Uses

Bait

Crayfish are commonly sold and used as bait, either live or with only the tail meat, and are good at attracting channel catfish, largemouth bass, pike and muskie. However, live crayfish may sometimes have their claws removed in order to prevent their keeping fish from biting the hook. Crayfish also easily fall off the hook, so casting should be slow.

The result of using crayfish as bait has led to various ecological problems at times. According to a report prepated by Illinois State University, on the Fox River and Des Plaines River watershed, "The rusty crayfish (used as bait) has been dumped into the water and its survivors outcompete the native clearwater crayfish".^[13] This situation has been repeated elsewhere, as the crayfish bait eliminates native species.^[14]

As zebra mussels have also been known to attach themselves to the crayfish bait, this is one of the ways it has spread to different waterways.^[15]

Food

Crayfish are eaten all over the world. Like other edible crustaceans, only a small portion of the body of a crayfish is edible. In most prepared dishes, such as soups, bisques and étouffées, only the tail portion is served. At crawfish boils or other meals where the entire body of the crayfish is presented, other portions may be eaten.

Claws of larger boiled specimens are often pulled apart to access the meat inside. Another favourite is to suck the head of the crayfish, as seasoning and flavour can collect in the fat of the boiled interior. A popular double entendre laden phrase heard around crawfish season in Louisiana derives from this practice: "suck the head; pinch the tail".^[16]

A common myth is that a crawfish with a straight tail died before it was boiled and is not safe to eat. In reality, crawfish that died before boiling can have curled tails as well as straight, as can those that were alive, and may very well be fine to eat. Boiled crawfish which died before boiling are safe to eat if they were kept chilled before boiling and were not dead for a long time. (This does not mean that a sack of crawfish that are all dead should be boiled.) A much better test than the straight tail as to the edibility of any crawfish is the tail meat itself; if it is mushy, it is usually an indication that it should be avoided.^[17]

Like all crustaceans, crayfish are not kosher because they are aquatic animals that do not have both fins and scales.^[18] They are therefore not eaten by observant Jews.

China

The culinary popularity of crayfish swept across Mainland China in the late 1990s. Crayfish is generally served with Mala flavour (a combined flavour of Sichuan pepper and hot chili) or otherwise plainly steamed whole, to be eaten with a preferred sauce. In Beijing, the ma la flavoured crayfish (麻辣小龙虾) is shortened to "ma xiao" (麻小) and is often enjoyed with beer in a hot mid-summer evening.

France

In France, dishes with a base or garnish of crayfish (écrevisse) are frequently given the suffix à la Nantua.

Spain

In Spain, crayfish is called cangrejo de río (lit. "river crab"). They used to be widely consumed, especially in Castile and Aragon, but over-fishing and the introduction of non-native crayfish species lead to a dramatic decline in crayfish population. Nowadays they remain as a seasonal delicacy, usually stewed in tomato sauce.

Mexico

The Mexican crayfish is named locally as acocil and was a very important nutrition source of the ancient Mexican Aztec culture; now this kind of crayfish is consumed (mainly boiled) and prepared with typically Mexican sauces or condiments in central and southern Mexico.

Scandinavia

Crayfish is a popular dish in Scandinavia, and is by tradition primarily consumed during the fishing season in August. The boil is typically flavored with salt, sugar, ale, and large quantities of the flowers of the dill plant. While most Americans eat them warm, the Swedish and Finnish normally eat them cold.^[19] The catch of domestic freshwater crayfish, Astacus astacus, and even of a transplanted American species, Pacifastacus leniusculus, is very limited and to satisfy demand the majority of what is consumed has to be imported. Sales depended on imports from Turkey for several decades, but after a decline in supply, China and the United States are today the biggest sources of import.

United States

Louisiana crawfish are usually boiled live in a large pot with heavy seasoning (salt, cayenne pepper, lemon, garlic, bay leaves, etc.) and other items such as potatoes, corn on the cob, onions, garlic, mushrooms and sausage. There are many differing methods used to season a crawfish boil and an equal number of opinions on which one is correct.^[20] They are generally served at a gathering known as a crawfish boil. Other popular dishes in the Cajun and Creole cuisines of Louisiana include crawfish étouffée, crawfish pie, crawfish dressing, crawfish bread and crawfish beignets.^[21]

Nigeria

Crayfish are usually smoked, and occasionally sun-dried, and they form an indispensable food item in the diet of the people of the entire southern States in particular and Nigeria as a whole. It is the core of Nigerian cooking.

Pets

Crayfish are kept as pets in freshwater aquariums. They prefer foods like shrimp pellets or various vegetables but will also eat tropical fish food, regular fish food, algae wafers, and even small fish that can be captured by their claws, such as goldfish or minnows. Their disposition towards eating almost anything will also cause them to consume most aquarium plants in a fish tank; however, crayfish are fairly shy and may attempt to hide under leaves or rocks.

When keeping a crayfish as a pet, it is suggested they are provided with a hiding space. At night, some fish become less energetic and settle to the bottom. The crayfish might see this as a chance for an easy meal, or a threat, and injure or kill the fish with its claws. Crayfish are effective scavengers and will consume fish carcasses. They sometimes will consume their old exoskeleton after it has molted.

Since crayfish are accustomed to being around ponds or rivers they will have a tendency to shift gravel around on the bottom of the tank, creating mounds or trenches to emulate a burrow. Crayfish will often try to climb out of the tank, especially if an opening exists at the top that they can fit through. Crayfish kept as pets in the United States from local waters are usually kept with bluegill or bass rather than goldfish or other tropical/subtropical fish.

However, most species of dwarf crayfish, such as Cambarellus patzcuarensis will not destructively dig or eat live aquarium plants.^[22] They are also relatively non-aggressive and can even be kept safely with dwarf shrimp. Because of their very small size of 1.5 inches (38 mm) or less, some fish, such as loaches are often a threat to the crayfish rather than the other way around.

In some nations, such as the United Kingdom, United States, Australia, and New Zealand, imported alien crayfish are a danger to local rivers. The three species commonly imported to Europe from the Americas are Orconectes limosus, Pacifastacus leniusculus and Procambarus clarkii.^[12] Crayfish may spread into different bodies of water because specimens captured for pets in one river are often released into a different catchment. There is a potential for ecological damage when crayfish are introduced into non-native bodies of water (e.g., crayfish plague in Europe).

Production

Louisiana supplies 98% of the crayfish harvested in the United States. In 1987, Louisiana produced 90% of the crawfish in the world and 70% was consumed locally.^[23] 70%–80% of crawfish produced in Louisiana are red swamp crawfish with the remaining 20%–30% being white river crawfish.^[24]

References

Further reading

• Thomas Henry Huxley (1880). The Crayfish: an Introduction to the Study of Zoology. New York: D. Appleton & Co.. http://www.archive.org/details/crayfishintroduc00huxl. 
• Lance Gilbertson; Zoology Lab Manual; McGraw Hill Companies, New York; ISBN 0-07-237716-X (fourth edition, 1999)
• Sterling K. Johnson and Nathan K. Johnson. 2008. Texas Crawdads. College Station, Texas. ISBN 978-0-9801103-0-2 available from Crawdad Club Designs
• Jerry G. Walls, "Crawfishes of Louisiana". Baton Rouge, LA. Florida State University Press, 2009 ISBN 978-0-8071-3409-2

External links

• International Association of Astacology (IAA)
• Louisiana Crawfish Research and Promotion Board
• Crayfish Moulting Video
• An Appalachian Crayfish Photo Gallery

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