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Biology

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Feeding at night on worms, aquatic insects, molluscs and plants, the noble crayfish spends the day resting in a burrow. It undergoes periodic moults, shedding the hard exoskeleton in order to grow slightly larger, and then forming a new shell. Sexual maturity is reached during the fourth year of life, and breeding takes place between October and November. The fertilised eggs are carried by the female, attached to her legs, over the winter until May, when they hatch and disperse. Both juvenile and adult noble crayfish are preyed upon by mink, eel, perch, pike, otter, and muskrat (2).
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Conservation

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Efforts to reintroduce the noble crayfish have been hindered by the presence of the signal crayfish, which competes for food resources, although in Norway some recent reintroductions look promising (5). In most European countries limits have been set for the trapping of noble crayfish, including restricting trapping to a period of about three months, and setting a minimum crayfish length of 10 cm. In some areas, trapping is completely prohibited. Elimination, or at least reduction, of signal crayfish populations, and protection of crayfish habitat are required to allow the noble crayfish to recover (2).
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Description

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This crustacean varies in colour from green or blue to brown and sometimes black. The undersides of the claws are dark red (2). The head and internal organs of all crayfish are protected by the carapace and the six segments of the abdomen are individually encased with a flexible membrane between them to allow movement. Crayfish have a pair of large claws at the front end, followed by four pairs of walking legs and then four pairs of small swimming legs called swimmerets. These swimmerets are covered with fine hairs to which the female attaches her eggs. A central tail flap is surrounded by four other flaps that are used to move the crayfish rapidly through the water, as well as curling up to form a brood chamber. There are two eyes on the end of eyestalks, but the senses of touch and taste are far more important, and are perceived using a pair of large feelers (or antennae) and a pair of small, fine, centrally located feelers (or antennules).
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Habitat

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A freshwater invertebrate, the noble crayfish is found along the banks of well oxygenated streams, rivers, lakes and ponds (2).
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Range

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Previously prolific throughout Europe, the noble crayfish now has a scattered distribution through northern Europe and western Russia (1) (2).
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Status

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The noble crayfish is classified as Vulnerable (VU) on the IUCN Red List (1). It is listed under Appendix III of the Berne Convention on the Conservation of European Wildlife and Natural Habitats (3) and on Annex V of the EC Habitats Directive (4).
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Threats

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Considered to be the finest edible crayfish, the noble crayfish was once abundant in Europe, but was expensive to buy. The American 'signal crayfish' (Pacifastacus leniusculus) was introduced to European waterways as a cheaper alternative, but the presence of this species was to have disastrous effects on the noble crayfish. An outbreak of crayfish plague, carried by the signal crayfish, spread through populations of all of Europe's Astacus species. Caused by the freshwater fungus Aphanomyces astaci, crayfish plague infects and kills the noble crayfish, leaving the resistant signal crayfish unharmed (3). Dredging of waterways has further threatened Astacus crayfish species as it leaves the water cloudy and disturbs the habitat. Acid rain, also causing a decrease in water quality, is thought to be responsible for a decline in breeding success, as the egg cases of young crayfish are unable to form properly (2).
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Astacus astacus

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Astacus astacus, the European crayfish, noble crayfish, or broad-fingered crayfish, is the most common species of crayfish in Europe, and a traditional food source. Like other true crayfish, A. astacus is restricted to fresh water, living only in unpolluted streams, rivers, and lakes. It is found from France throughout Central Europe, to the Balkan Peninsula, and north as far as Scandinavia and Finland, and Eastern Europe. Males may grow up to 16 cm long, and females up to 12 cm.[3]

Ecology

Noble crayfish can vary greatly in colour.[4]

European crayfish feed on worms, aquatic insects, molluscs, and plants.

They are nocturnal, spending the day resting in a burrow. They prefer habitats with high levels of shelter availability.[1] The waters they are found in tend to be soft-bottomed with some sand, and they do not tend to be found in muddy water.[1]

A. astacus become sexually mature after three to four years and a series of moults, and breed in October and November. Fertilised eggs are carried by the female, attached to her pleopods, until the following May, when they hatch and disperse.

The main predators of A. astacus, both as juveniles and adults, are European mink, eels, perch, pike, Eurasian otters, and muskrats.[3] There is also some risk of predation via cannibalism.[1]

A. astacus is sensitive to dips in oxygen levels in the water it inhabits, which makes it particularly vulnerable to eutrophication. However, they are capable of tolerating lower calcium levels than most other species of crayfish.[1]

A. astacus is regarded as a keystone species in the environments it inhabits. Crayfish are an important part of the freshwater food web as they provide a source of food to many aquatic species and boost primary productivity by foraging on freshwater plants. The loss of crayfish in a freshwater environment is known to cause macrophyte growth, which can be a cause for eutrophication and an overall degradation in water quality.[5]

Consumption

This species was once abundant in Europe, although it was expensive to buy, and is considered to be the finest edible crayfish.[3] It is, however, susceptible to the crayfish plague carried by the invasive North American species signal crayfish (Pacifastacus leniusculus), so is listed as a vulnerable species on the IUCN Red List.[1] Since the introduction of the plague, A. astacus has dropped to about 5% of its preexisting population.[5]

A golden grayfish pictured in the coat of arms of Oulainen

Documentation of the consumption of A. astacus dates back to the Middle Ages, when it was popular among the Swedish nobility, spreading to all social classes by the 17th and 18th centuries due to its ready availability. The crayfish are collected from the wild in traps, a practice which is being replaced by more intensive aquaculture of the signal crayfish in man-made ponds.[6] The consumption of crayfish is an important part of traditional Nordic culture, including the crayfish party (Swedish: kräftskiva; Finnish: rapujuhlat), a feast to mark the end of summer.[6]

Hundreds of smaller or larger lakes were once found in the northern Moldavia, used for growing A. astacus meant for consumption during the extended fasting periods of the Orthodox Christian calendar. The area of the former Dorohoi County was one such area, and this legacy was visible in the county's historical coat of arms, featuring an A. astacus (Romanian: rac).

Astacin

Astacins are a family of digestive enzymes, discovered in the 1990s, which were first isolated from A. astacus. More than 20 enzymes of this group have since been discovered in animals from Hydra to humans.[7]

References

  1. ^ a b c d e f L. Edsman; L. Füreder; F. Gherardi & C. Souty-Grosset (2010). "Astacus astacus". The IUCN Red List of Threatened Species. IUCN. 2010: e.T2191A9338388. doi:10.2305/IUCN.UK.2010-3.RLTS.T2191A9338388.en.
  2. ^ a b Crandall, Keith A; De Grave, Sammy (2017). "An updated classification of the freshwater crayfishes (Decapoda: Astacidea) of the world, with a complete species list". Journal of Crustacean Biology. 37 (5): 615–653. doi:10.1093/jcbiol/rux070.
  3. ^ a b c "Noble crayfish (Astacus astacus)". ARKive. Archived from the original on March 28, 2008. Retrieved May 6, 2007.
  4. ^ Peter Scheffel & Bernd Sceiba. Plants and Animals of Central Europe (Pflanzen und Tiere).
  5. ^ a b "Value of Biodiversity - Documenting EU examples where biodiversity loss has led to the loss of ecosystem services". ieep.eu. Retrieved 2022-10-14.
  6. ^ a b "Astacus astacus". Slow Food Foundation. Retrieved December 18, 2019.
  7. ^ J. S. Bond & R. J. Benyon (1995). "The astacin family of metalloendopeptidases". Protein Science. 4 (7): 1247–1261. doi:10.1002/pro.5560040701. PMC 2143163. PMID 7670368.
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Astacus astacus: Brief Summary

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Astacus astacus, the European crayfish, noble crayfish, or broad-fingered crayfish, is the most common species of crayfish in Europe, and a traditional food source. Like other true crayfish, A. astacus is restricted to fresh water, living only in unpolluted streams, rivers, and lakes. It is found from France throughout Central Europe, to the Balkan Peninsula, and north as far as Scandinavia and Finland, and Eastern Europe. Males may grow up to 16 cm long, and females up to 12 cm.

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