Crayfish
2008/9 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and Fish
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Crayfish, often referred to as crawfish or crawdads, are freshwater crustaceans resembling small lobsters, to which they are closely related. They breathe through 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. Some crayfish have been found living as much as 3 m (10 feet) underground.
In New Zealand, the name crayfish (or cray) refers to a saltwater spiny lobster, of the type Jasus that is indigenous to much of southern Oceania. And crayfish are called freshwater crays or koura, the Māori name for the animal.
The study of crayfish is called astacology .
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 , mudbugs 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 .
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. A crayfish is usually 7.5 centimeters long.
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 . 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.
Europe is home to seven species of crayfish in the genera Astacus and Austropotamobius.
Cambaroides is native to Japan and eastern mainland Asia.
Molting
Crayfish moult as they grow because their hard exoskeletons do not allow much room for expansion. Baby crayfish can moult daily, but as they grow older the regularity of moults decreases to weeks or months. The first few days after moulting, a crayfish's skin is very soft and it is very vulnerable to attacks from other animals and crayfish.
Early signs of moulting include lack of appetite and slowing 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 eats the old shell to replace the lost calcium and strengthen the weakened carapace.
Crayfish as a dish
Crayfish are eaten in Europe, China, Africa, 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 écrevisses.
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, maize, onions, garlic, and sausage. 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 , 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 flavoured 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 Malay 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.
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, however, 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 boiled interior. A popular double entendre laden phrase heard around crawfish season in Louisiana derives from this practice: "Suck the head, eat the tail" .
Crayfish as 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, 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, one must provide 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 an exoskeleton after it is moulted. Crayfish are great escape artists and will try to climb out of the tank, so any holes in the hood should be covered.
In some nations, such as England, 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. Crayfish may spread into different bodies of water because specimens captured for pets in one river are often flung back into a different one. There is a potential for ecological damage when crayfish are introduced into nonnative bodies of water. Crayfish kept as pets should never be released to the wild due to this potential hazard to the ecosystem.
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.
Other
The Moche people of ancient Peru worshiped animals and often depicted crayfish in their art.