Crayfish

The greatest diversity of crayfish species is found in southeastern 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]

In 1983, Louisiana designated the crayfish, or crawfish as they are commonly called, as its official state crustacean.[10] Louisiana produces 100 million pounds of crawfish per year with the red swamp and white river crawfish being the main species harvested.[11] Crawfish are a part of Cajun culture dating back hundreds of years.[12] A variety of cottage industries have developed as a result of commercialized crawfish iconology. Their products include crawfish attached to wooden plaques, T-shirts with crawfish logos, and crawfish pendants, earrings, and necklaces made of gold or silver.[13]

Australia has over 100 species in a dozen genera. It is home to the world's three largest freshwater crayfish:

• the Tasmanian giant freshwater crayfish Astacopsis gouldi, which can achieve a mass over 5 kg (11 lb) and is found in rivers of northern Tasmania[14]
• the Murray crayfish Euastacus armatus, which can reach 2.5 kg (5.5 lb), although reports of animals up to 3 kg (6.6 lb) have been made. It is found in much of the southern Murray-Darling basin.[15]
• the marron from Western Australia (now believed to be two species, Cherax tenuimanus and C. cainii) which may reach 2.2 kg (4.9 lb)

Many of the better-known Australian crayfish are of the genus Cherax, and include the common yabby (C. destructor), western yabby (C. preissii), and red-claw crayfish (C. quadricarinatus).[16]

The marron species C. tenuimanus is critically endangered, while other large Australasian crayfish are threatened or endangered.

In New Zealand, two species of Paranephrops are endemic, and are known by the Māori name kōura.[17]

In Australia, New Zealand, and South Africa,[18] the term "crayfish" or "cray" generally refers to a saltwater spiny lobster, of the genus Jasus that is indigenous to much of southern Oceania,[19] while the freshwater species are usually called yabbies or kōura, from the indigenous Australian and Māori names for the animal, respectively, or by other names specific to each species. Exceptions include western rock lobster (of the Palinuridae family) found on the west coast of Australia; the Tasmanian giant freshwater crayfish (from the Parastacidae family) found only in Tasmania; and the Murray crayfish found along Australia's Murray River.

In Singapore, the term crayfish typically refers to Thenus orientalis, a seawater crustacean from the slipper lobster family.[20][21][22] True crayfish are not native to Singapore, but are commonly found as pets, or as an invasive species (Cherax quadricarinatus) in the many water catchment areas, and are alternatively known as freshwater lobsters.[23][24]

Crayfish are eaten worldwide. Like other edible crustaceans, only a small portion of the body of a crayfish is eaten. 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, such as the claw meat, may be eaten.

As of 2005, Louisiana supplies 95% of the crayfish harvested in the U.S.[31] In 1987, Louisiana produced 90% of the crayfish harvested in the world, 70% of which were consumed locally.[32] In 2007, the Louisiana crawfish harvest was about 54,800 tons, almost all of it from aquaculture.[33] About 70–80% of crayfish produced in Louisiana are Procambarus clarkii (red swamp crawfish), with the remaining 20–30% being Procambarus zonangulus (white river crawfish).[34] Optimum dietary nutritional requirement of freshwater crayfish, or crayfish nutrient specifications are now available for aquaculture feed producers [35]

Like all crustaceans, crayfish are not kosher because they are aquatic animals that do not have both fins and scales.[36] They are therefore not eaten by observant Jews.[37]

Crayfish are preyed upon by a variety of ray-finned fishes,[38] and are commonly used as bait, either live or with only the tail meat. They are a popular bait for catching catfish,[39] largemouth bass, smallmouth bass, striped bass,[40] perch, pike[41] and muskie. When using live crayfish as bait, anglers prefer to hook them between the eyes, piercing through their hard, pointed beak which causes them no harm; therefore, they remain more active.[42]

When using crayfish as bait, it is important to fish in the same environment where they were caught. An Illinois State University report that focused on studies conducted on the Fox River and Des Plaines River watershed stated that rusty crayfish, initially caught as bait in a different environment, were dumped into the water and "outcompeted the native clearwater crayfish."[43] Other studies confirmed that transporting crayfish to different environments have led to various ecological problems, including the elimination of native species.[44] Transporting crayfishes as live bait has also contributed to the spread of zebra mussels in various waterways throughout Europe and North America, as they are known to attach themselves to exoskeleton of crayfishes.[45][46][47]

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 small fish that can be captured with their claws. A report by the National Park Service[48] as well as video and anecdotal reports by aquarium owners[49] indicate that crayfish will eat their molted exoskeleton "to recover the calcium and phosphates contained in it."[48] As omnivores, crayfish will eat almost anything; therefore, they may explore the edibility of aquarium plants in a fish tank. However, most species of dwarf crayfish, such as Cambarellus patzcuarensis, will not destructively dig or eat live aquarium plants.[50]

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.[28] 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, or the introduction of the common yabby (Cherax destructor) into drainages east of the Great Dividing Range in Australia.[51]

The Protivin brewery in the Czech Republic uses crayfish outfitted with sensors to detect any changes in their bodies or pulse activity in order to monitor the purity of the water used in their product. The creatures are kept in a fish tank that is fed with the same local natural source water used in their brewing. If three or more of the crayfish have changes to their pulses, employees know there is a change in the water and examine the parameters.[52]

Scientists also monitor crayfish in the wild in natural bodies of water to study the levels of pollutants there.[52][53][54]