| Crayfish | |
|---|---|
 | |
| Paranephrops species (Parastacidae) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Order: | Decapoda |
| Suborder: | Pleocyemata |
| (unranked): | Reptantia |
| Infraorder: | Astacidea |
| Superfamilies andfamilies | |
Crayfish[a] are freshwatercrustaceans belonging to the infraorderAstacidea, which also containslobsters. Taxonomically, they are members of thesuperfamiliesAstacoidea andParastacoidea. They breathe through feather-likegills. Some species are found in brooks and streams, wherefresh water is running, while others thrive inswamps, ditches, andpaddy fields. Most crayfish cannot toleratepolluted water, although some species, such asProcambarus clarkii, are hardier. Crayfish feed on animals and plants, either living ordecomposing, anddetritus.[1]
The term "crayfish" is applied to saltwater speciesin some countries.
The name "crayfish" comes from theOld French wordescrevisse (Modern Frenchécrevisse).[2][3] The word has been modified to "crayfish" by association with "fish" (folk etymology).[2] The largelyAmerican variant "crawfish" is similarly derived.[2]
Some kinds of crayfish are known locally aslobsters,[4] crawdads,[5] mudbugs,[5] andyabbies. In theEastern United States, "crayfish" is more common in the north, while "crawdad" is heard more in central and southwestern regions, and "crawfish" farther south, although considerable overlaps exist.[6]
The study of crayfish is called astacology.[7]
The body of adecapodcrustacean, such as a crab, lobster, or prawn (shrimp), is made up of twentybody segments grouped into two main body parts, thecephalothorax and theabdomen. Each segment may possess one pair ofappendages, although in various groups, these may be reduced or missing. On average, crayfish grow to 17.5 cm (6.9 in) in length. Walking legs have a small claw at the end.[8]
Crayfish are opportunisticomnivorous scavengers, with the ability to filter and process mud.[9] Inaquaculture ponds usingisotope analysis they were shown to build body tissue selectively from the animal protein portion of pelleted food and not the other components of the pellet.[10]
They have the potential to eat most foods, even nutrient poor material such as grass, leaves, and paper, but can be highly selective and need variety to balance their diet. The personalities of the individual crayfish can be a key determinant in the food preference behaviour in aquaria.[citation needed]
Crayfish all over the world can be seen in anecological role ofbenthic dwellers, so this is where most of their food is obtained – at the sediment/water interface in ponds, lakes, swamps, or burrows. When the gut contents are analysed, most of the contents is mud: fine particulate organic matter (FPOM) and mixed particles of lignin and cellulose (roots, leaves, bark, wood).[11] Some animal material can also be identified, but this only contributes a small portion of the diet by volume.
They feed on submerged vegetable material at times, but their ability to catch large living animal material is restricted. They can feed oninterstitial organisms if they can be grasped in the small feeding claws. They can be lured into traps with an array of baits from dog biscuits, fish heads, meat, etc., all of which reinforces the fact that they are generalist feeders.
On a day-to-day basis, they consume what they can acquire in their immediate environment in limited space and time available -detritus. At a microbial level, the FPOM has a high surface area of organic particles and consists of a plethora ofsubstrate andbacteria,fungi,micro-algae,meiofauna, partially decomposed organic material and mucus. This mucus or "slime" is abiofilm and can be felt on the surface of leaves and sticks. Also crayfish have been shown to becoprophagic – eating their own faeces, they also eat their ownexuviae (moultedcarapace) and each other.[10] They have even been observed leaving the water to graze.[12]
Detritus or mud is a mixture of deadplankton (plant and animal), organic wastes from thewater column, and debris derived from the aquatic and terrestrial environments. Mostly detritus is in the end phase of decomposition and is recognised as black organic mud. The crayfish usually ingest the material in only a few minutes, as distinct from grazing for many hours. The material is mixed with digestive fluids and sorted by size. The finer particles follow a slower and more exacting route through to thehindgut, compared to the coarser material. The coarser material is eliminated first and often reappears in approximately 10 to 12 hours, whereas the finer material is usually eliminated from 16 to 26 hours after ingestion.[13]
All waste products coming out through the hindgut are wrapped in aperitrophic membrane, so they look like a tube. Such an investment in the wrapping of the microbial free faeces in a protein rich membrane is most likely the reason they are coprophagic. Such feeding behaviour based on selection, ingestion, and extreme processing ensures periodic feeding, as distinct from continuous grazing. They tend to eat to satiation and then take many hours to process the material, leaving minimal chance of having more room to ingest other items. Crayfish usually have limited home range and so they rest, digest, and eliminate their waste, most commonly in the same location each day.
Feeding exposes the crayfish to risk of predation, and so feeding behaviour is often rapid and synchronised with feeding processes that reduce such risks – eat, hide, process and eliminate.
Knowledge of the diet of these creatures was considered too complex since the first book ever written in the field of zoology,The Crayfish byT.H. Huxley (1879), where they were described as "detritivores". This is why most researchers have not attempted to understand the diet of freshwater crayfish. The most complex study which matched the structure and function of the whole digestive tract with ingested material was performed in the 1990s by Brett O'Brien onmarron,[13] the least aggressive of the larger freshwater crayfish with aquaculture potential, similar to redclaw and yabbies.
Crayfish are closely related tolobsters, and together they belong to theinfraorderAstacidea. Theirphylogeny can be shown in the simplifiedcladogram below:[14][15][16]
Fourextant (living)families of crayfish are described, three in theNorthern Hemisphere and one in theSouthern Hemisphere. The Southern Hemisphere (Gondwana-distributed) familyParastacidae, with 14 extant genera and two extinct genera, live(d) inSouth America,Madagascar, andAustralasia. They are distinguished by the absence of the first pair ofpleopods.[17] Of the other three Northern Hemisphere families (grouped in thesuperfamilyAstacoidea), the four genera of the familyAstacidae live in westernEurasia and westernNorth America, the 15 genera of the familyCambaridae live in easternNorth America, and the single genus ofCambaroididae live in easternAsia.[15]
The greatest diversity of crayfish species is found in southeastern North America, with over 330 species in 15 genera, all in the family Cambaridae. A further genus of astacid crayfish is found in thePacific Northwest and the headwaters of some rivers east of theContinental Divide. Many crayfish are also found in lowland areas where the water is abundant incalcium, and oxygen rises from underground springs.[18] Crayfish are also found in some non-coastal wetlands; eight species of crayfish live inIowa,[19] for example.
In 1983,Louisiana designated the crayfish, or crawfish as they are commonly called, as its official state crustacean.[20] Louisiana produces 100 million pounds (45 million kilograms) of crawfish per year with thered swamp andwhite river crawfish being the main species harvested.[21] Crawfish are a part ofCajun culture dating back hundreds of years.[22] A variety of cottage industries have developed as a result of commercialized crawfish iconography. Their products include crawfish attached to wooden plaques, T-shirts with crawfish logos, and crawfish pendants, earrings, and necklaces made of gold or silver.[23]
Australia has over 100 species in a dozengenera. It is home to the world's three largest freshwater crayfish:
Many of the better-known Australian crayfish are of the genusCherax, and include thecommon yabby (C. destructor), western yabby (C. preissii), andred-claw crayfish (C. quadricarinatus).[26]
The marron speciesC. tenuimanus iscritically endangered, while other large Australasian crayfish are threatened or endangered.
InNew Zealand, two species ofParanephrops are endemic, and are known by theMāori namekōura.[27]
In Australia, New Zealand, andSouth Africa,[28] the term "crayfish" or "cray" generally refers to a saltwaterspiny lobster, of the genusJasus that is indigenous to much of southernOceania,[29] while thefreshwater species are usually calledyabbies orkōura, from theindigenous Australian and Māori names for the animal, respectively, or by other names specific to each species. Exceptions includewestern rock lobster (of thePalinuridae family) found on the west coast of Australia (it is a spiny lobster, but not ofJasus); theTasmanian giant freshwater crayfish (from theParastacidae family and therefore a true crayfish) found only in Tasmania; and theMurray crayfish found along Australia'sMurray River.[citation needed]
InSingapore, the term crayfish typically refers toThenus orientalis, a seawater crustacean from theslipper lobster family.[30][31][32] 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 asfreshwater lobsters.[33]
In the United Kingdom and Ireland, the terms crayfish or crawfish commonly refer to theEuropean spiny lobster, a saltwater species found in much of the East Atlantic and Mediterranean.[34] The only true crayfish species native to the British Isles is the endangeredwhite clawed crayfish.[35][36]
Fossil burrows very similar in construction to those of modern crayfish and likely produced by early crayfish are known from theEarly Permian (~300-270 million years ago) of equatorialPangea, in what is now North America (Washington Formation), and Europe (Sardinia). The oldest body fossils assigned to crayfish are known from theLate Triassic (~230-200 million years ago)Chinle Formation of North America, assigned to the species "Enoploclytia"porteri andCamborygma eumekenomos, which are not assigned to any modern families. An indeterminate member of the modern familyCambaridae is known from the Late JurassicMorrison Formation of North America.[37] The earliest records of other modern families date to the Early Cretaceous, including theparastacidPalaeoechinastacus from Australia which is 115 million years old,[38] thecambaroididPalaeocambarus from theYixian Formation of China which is likely around 120 million years old (Barremian-Aptian),[39] and theastacid"Austropotamobius" llopisi from theLas Hoyas site inSpain (Barremian).[40]
Crayfish are susceptible to infections such ascrayfish plague and to environmental stressors including acidification. In Europe, they are particularly threatened by crayfish plague, which is caused by the North Americanwater moldAphanomyces astaci. This water mold was transmitted to Europe when North American species of crayfish were introduced.[41] Species of the genusAstacus are particularly susceptible to infection, allowing the plague-coevolvedsignal crayfish (native to western North America) to invade parts ofEurope.[42]
Acid rain can cause problems for crayfish across the world. In whole-ecosystem experiments simulating acid rain at theExperimental Lakes Area inOntario, Canada, crayfish populations crashed – probably because theirexoskeletons are weaker inacidified environments.[43]
In several countries, particularly in Europe, native species of crayfish are under threat by imported species, particularly the signal crayfish (Pacifastacus leniusculus).[44][45] Crayfish are also considered an invasive predatory species, endangering native European species such as theItalian agile frog and thepainted frog inMalta.[46]
-in-freshwater-aquarium-with-apple-snail.jpg)
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 andétouffées, only the tail portion is served. Atcrawfish boils or other meals where the entire body of the crayfish is presented, other portions, such as the claw meat, may be eaten.[citation needed]
Research shows that crayfish do not die immediately when boiled alive, and respond to pain in a similar way to mammals. Then the stress hormone cortisol is released and this leads to the formation of lactic acid in the muscles, which makes the meat taste sour. Crayfish can be cooked more humanely by first freezing them unconscious for a few hours, then destroying the central nervous system along their abdomen by cutting the crayfish lengthwise with a long knife down the center of the crayfish before cooking it.[47]
Global crayfish production is centered in Asia, primarily China. In 2018, Asian production accounted for 95% of the world's crawfish supply.[48]
Crayfish is part ofSwedish cuisine and is usually eaten in August at specialcrayfish parties (Swedish:Kräftskiva). Documentation of the consumption of crayfish dates to at least the 16th century. On the Swedish west coast,Nephrops norvegicus (Havskräfta,lit. 'sea crayfish') is more commonly eaten while various freshwater crayfish are consumed in the rest of the country. Prior to the 1960s, crayfish was largely inaccessible to the urban population in Sweden and consumption was largely limited to the upper classes or farmers holding fishing rights in fresh water lakes. With the introduction of import of frozen crayfish the crayfish party is now widely practiced across all spheres in Sweden and among theSwedish-speaking population of Finland.[49]
In the United States, crayfish production is strongly centered inLouisiana, with 93% of crayfish farms located in the state as of 2018.[50] In 1987, Louisiana produced 90% of the crayfish harvested in the world, 70% of which were consumed locally.[51] In 2007, the Louisiana crayfish harvest was about 54,800 tons, almost all of it fromaquaculture.[52] About 70–80% of crayfish produced in Louisiana areProcambarus clarkii (red swamp crawfish), with the remaining 20–30% beingProcambarus zonangulus (white river crawfish).[53] Optimum dietary nutritional requirement of freshwater crayfish, or crayfish nutrient specifications are now available for aquaculture feed producers[54]
Like all crustaceans, crayfish are notkosher because they are aquatic animals that do not have bothfins andscales.[55] They are therefore not eaten by observantJews, and some Christian denominations.[56][57]
Crayfish are preyed upon by a variety ofray-finned fishes,[58] and are commonly used asbait, either live or with only the tail meat. They are a popular bait for catchingcatfish,[59]largemouth bass,smallmouth bass,striped bass,[60]perch,pike[61] andmuskie. 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.[62]
When using crayfish as bait, it is important to fish in the same environment where they were caught. AnIllinois State University report that focused on studies conducted on theFox River andDes Plaines River watershed stated thatrusty crayfish, initially caught as bait in a different environment, were dumped into the water and "outcompeted the native clearwater crayfish".[63] Other studies confirmed that transporting crayfish to different environments has led to various ecological problems, including the elimination of native species.[64] Transporting crayfish as live bait has also contributed to the spread ofzebra mussels in various waterways throughout Europe and North America, as they are known to attach themselves to exoskeleton of crayfishes.[65][66][67]
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 theNational Park Service[68] as well as video and anecdotal reports by aquarium owners[69] indicate that crayfish will eat their moulted exoskeleton "to recover the calcium and phosphates contained in it."[68] 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 asCambarellus patzcuarensis, will not destructively dig or eat live aquarium plants.[70]
In some nations, such as theUnited Kingdom,United States,Australia, andNew Zealand, imported alien crayfish are a danger to local rivers. The three most widespread American species invasive in Europe areFaxonius limosus,Pacifastacus leniusculus andProcambarus clarkii.[41] 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.[71]
Somepublic schools in the United States keep live crayfish in the classroom and have the students take care of them in order to give the students a greater understanding of the creatures.[72]
The Protivin brewery in theCzech 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.[73]
Scientists also monitor crayfish in the wild in natural bodies of water to study the levels of pollutants there.[73][74][75]
Isotopic analysis confirmed limited nocturnal observations that these individuals were consuming living terrestrial plants
Subgroups of orderDecapoda | |||||||||||||||||||||||||
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| Pleocyemata |
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