Crayfish
From Free net encyclopedia
- For the crustaceans commonly known as "sea crayfish", see spiny lobster.
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Crayfish, sometimes called crawfish, or crawdads 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, 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".
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The name crayfish
The name "crayfish" does not derive from the word "fish", but rather from the Old French word escrevisse (Modern French écrevisse) meaning "crevice" and referring to the habit of the animal. The word has been modified to "crayfish" by association with "fish". The largely American variant "crawfish" is similarly derived. (This derivation is an example of folk etymology.)
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, carmels, yabbies, or spoondogs.
Geographical distribution and classification
Image:Krafta pa brygga.jpg 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 <ref>Template:Cite journal2</ref>. 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 250 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.
Image:Crayfish-Astacus astacusP1002890.JPG
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, rather than to 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 stengthen the weakened carapace.
Crayfish as a dish
Crayfish are eaten in Europe and China, but they are perhaps most popular in Louisiana, where the standard culinary term is crawfish. They are usually boiled in a huge pot with heavy seasoning (cayenne pepper, paprika, etc.) and other items such as potatoes, sausage, corn, onions and garlic bulbs.
They are also served in various American dishes in restaurants around the United States. They may be fried or blackened. There are also specific preparations for crawfish in cajun and creole food, the best-known of which are crawfish étouffée, crawfish po' boy, crawfish pie, and crawfish beignets.
Crayfish is a popular dish in Sweden and Finland, and is by tradition primarily consumed during the fishing season in August. The boil is typically flavored with salt, sugar, and the flowers of the dill plant. The catch of domestic fresh water crayfish, and even of an implanted American species 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. On the western coast of Sweden, many tend to prefer the larger salt water crayfish, which is caught in the North Sea (see Swedish cuisine).
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.
Crayfish as pets
Crayfish are sometimes kept as pets in freshwater aquariums. They prefer foods like shrimp pellets or various vegetables but will eat most leftover fish food. They also have a big appetite for plants and will eat most aquarium plants. They can be aggressive and may attempt to eat fish. At night, some fish become less energetic and settle to the bottom. The crayfish might see it as a danger and hurt or kill it with its claws. 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, catching and keeping crayfish as pets is one of the main means of the spread of destructive species - since they are often flung back into a different river. Crayfish are also used as fishing bait and as live food for larger species of aquarium fish, oscars, for example. However, crayfish are actually fairly shy and may often attempt to hide under leaves or rocks. If you are going to keep a crayfish as a pet, remember to give it some hiding space
Crayfish as bait
Crayfish are commonly sold as bait fish to sport anglers in the United States. They are primarilly used as bait for bass. This trade has helped many species to expand beyond their natural range, including the rusty crayfish (Orconectes rusticus), which is considered invasive in its expanded range.
External links
- Crayfish forum
- A rare crayfish moulting video
- Crawfish recipes at RealCajunRecipes.com
- International Association of Astacology
- Crayfish Page
References
- Gilbertson, Lance; Zoology Lab Manual; McGraw Hill Companies, New York; ISBN 0-07-237716-X (fourth edition, 1999)
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