Crayfish

For the crustaceans commonly known as "sea crayfish", see spiny lobster.

Crayfish
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
Infraorder:	Astacidea
Superfamily:	Astacoidea Latreille, 1802 Parastacoidea Huxley, 1879
Families
Astacoidea   Astacidae   Cambaridae Parastacoidea   Parastacidae

Crayfish, often referred to as crawfish or crawdad, are freshwater crustaceans resembling small lobsters, to which they are closely related. They are found in bodies of fresh 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. Some crayfish have been found living as much as 3 m (10 feet) underground.

The study of crayfish is called astacology .

The anatomy of crayfish may be found in the article "decapod anatomy".

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.

In New Zealand the name crayfish (or cray) refers to a spiny lobster, and crayfish are called freshwater crays or koura, the Māori name for the animal.

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

Geographical distribution and classification

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A crayfish from a Swedish lake

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 . 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.

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.

Australasia is another centre of crayfish diversity, with 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 crayfish, Astacopsis gouldi, which can achieve a mass in excess of 3 kilograms, is found in the rivers of northern Tasmania.

Madagascar has a single (endemic) crayfish species, Astacopsis madagascarensis.

Astacus astacus

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

Cambaroides is native to Japan and eastern mainland Asia.

Moulting in crayfish

Crayfish also need to moult as they grow because their hard exoskeletons do not allow much room for expansion. Baby crayfish can moult on a daily basis but as they grow older, the regularity of moults decreases to a period of weeks or even months. The first few days after a moult, a crayfish's skin is very soft and it is very vulnerable to attacks from other animals and crayfish.

The early signs of moulting include lack of appetite and a slow down in activity. During this period the crayfish ingests calcium into an internal organ, not into the exoskeleton.

When the crayfish is ready to moult, it will try to find a hiding spot. Then it will move onto its back and begin fanning its pincers, legs and swimmerets (under the tail) in order to get as much oxygen as possible. The carapace will begin to crack behind the head; the new appendages then pierce the old shell; and then after about five minutes, a sudden, violent movement will detach the old shell from the crayfish .

The freshly moulted crayfish will invariably be larger as part of the growing process, but is vulnerable on several fronts. Firstly, the shell is very soft and vulnerable to predators, including other crayfish and fish. The crayfish needs to eat the old shell to replace the lost calcium and strengthen the weakened carapace.

Crayfish as a dish

Boiled crayfish

Crayfish are eaten in Europe, China, Australia and the United States. 98% of the crayfish harvested in the United States come from Louisiana, where the standard culinary terms are crawfish or ecrevisses.

Crayfish in Louisiana 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, onions, garlic, and sausage. They are generally served at a gathering known as a crawfish boil. Other popular crayfish dishes in the Cajun and Creole cuisines of Louisiana include crawfish étouffée, crawfish pie, crawfish bread, and crawfish beignets , and crayfish are an ingredient in chicken Marengo.

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. 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.

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.

In China, the culinary popularity of crayfish swept across Mainland China in the late 1990s. Crayfish is generally served in with ma la (麻辣) flavor (a combined flavor of Sichuan pepper and hot chili) or otherwise plainly steamed whole, to be eaten with a preferred sauce. In Beijing, the Ma La flavored 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.

Like other edible crustaceans, only 35% of the body weight of a crayfish is edible. The remainder can either be used for decoration, or is discarded.

Crayfish as pets

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Crayfish in a freshwater aquarium

Crayfish are sometimes kept as pets in freshwater aquaria. They prefer foods like shrimp pellets or various vegetables but will also eat tropical fish food, algae wafers, and even small fish that come too close, such as goldfish or minnows. Their disposition towards eating almost anything will also cause them to consume most aquarium plants in a fishtank; however, crayfish are fairly shy and may attempt to hide under leaves or rocks. When keeping a crayfish as a pet, remember to give it a hiding space. At night, some fish become less energetic and settle to the bottom. The crayfish might see it as a chance for an easy meal, or a threat, and injure or kill it with its claws. If you have a crayfish living with other fish species, you will not need to scoop out as many dead fish, as crayfish are effective scavengers. Crayfish are great escape artists and may try to climb out of the tank so any holes in the hood should be covered. In nations where imported alien crayfish are a danger to rivers, such as England, United States, Australia, and New Zealand, crayfish spread because specimens captured for aquariums in one river are often flung back into a different one. Because of the potential ecological damage from nonnative crayfish, crayfish kept as pets should never be released to the wild. The most humane way to dispose of a live crayfish is to freeze it.

These guys are really neat pets! They are so cool. As they may be creepy, they are very interesting. They do bite though so be cautious!

Crayfish plague

Main article: 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 prone to infection, allowing the more resistant signal crayfish to invade parts of Europe.

Crayfish in popular culture

• The Pokemon Corphish and Crawdaunt are based on crayfish.
• The crawyfish is one of the fish that can be caught and donated to the museum in both the Animal Crossing for the Gamecube and for the DS. The fish itself can only be caught in the video games in ponds around the town and cannot be caught out at sea or in the river.

References

• Gilbertson, Lance; Zoology Lab Manual; McGraw Hill Companies, New York; ISBN 0-07-237716-X (fourth edition, 1999)