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Eels (Anguilliformes; /æŋˌɡwɪlɨˈfɔrmz/) are an order of fish which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators. The term "eel" (originally referring to the European eel) is also used for some other similarly shaped fish, such as electric eels and spiny eels, but these are not members of the Anguilliformes order.

Description

Eels are elongated fish, ranging in length from 5 cm (2.0 in) in the one-jawed eel (Monognathus ahlstromi)[dubious ] to 4 m (13 ft) in the slender giant moray. Adults range in weight from 30 grams (1.1 oz) to well over 25 kilograms (55 lb). They possess no pelvic fins, and many species also lack pectoral fins. The dorsal and anal fins are fused with the caudal or tail fin, forming a single ribbon running along much of the length of the animal.

Most eels live in the shallow waters of the ocean and burrow into sand, mud, or amongst rocks. A majority of eel species are nocturnal, and thus are rarely seen. Sometimes they are seen living together in holes, or "eel pits". Some species of eels also live in deeper water on the continental shelves and over the slopes deep as 4,000 m (13,000 ft). Only members of the Anguilla family regularly inhabit fresh water, but they too return to the sea to breed.

Eels begin life as flat and transparent larvae, or leptocephali. Eel larvae drift in the surface waters of the sea, feeding on marine snow, small particles that float in the water. Eel larvae then metamorphose into glass eels and then become elvers before finally seeking out their juvenile and adult habitats. Freshwater elvers travel upstream and are forced to climb up obstructions, such as weirs, dam walls, and natural waterfalls. Lady Colin Campbell found, at Ballisodare, the eel fisheries were greatly improved by the hanging of loosely plaited grass ladders over barriers, enabling the elvers to ascend.

The heaviest true eel is the European conger. The maximum size of this species has been reported as reaching a length of 3 m (10 ft) and a weight of 110 kg (240 lb). Other eels are longer but do not weigh as much, such as the slender giant moray which reaches 4 m (13 ft).

Classification

This classification follows FishBase in dividing the eels into 15 families. Additional families included in other classifications (notably ITIS and Systema Naturae 2000) are noted below the family with which they are synomized in the Fish Base system.

Identifying the origin of the freshwater species has been problematic. Genomic studies indicate they are a monophyletic group which originated among the deep-sea eels.

Suborders and families

Suborder Anguilloidei

  • Anguillidae (freshwater eels)
  • Chlopsidae (false morays)
  • Heterenchelyidae (mud eels)
  • Moringuidae (spaghetti eels)
  • Muraenidae (moray eels)
  • Myrocongridae (thin eels)
  • Protanguillidae

Suborder Congroidei

  • Colocongridae (worm eels)
  • Congridae (congers)
    • Including Macrocephenchelyidae
  • Derichthyidae (longneck eels)
    • Including Nessorhamphidae
  • Muraenesocidae (pike congers)
  • Nettastomatidae (duckbill eels)
  • Ophichthidae (snake eels)

Suborder Nemichthyoidei

  • Nemichthyidae (snipe eels)
  • Serrivomeridae (sawtooth eels)

Suborder Synaphobranchoidei

  • Synaphobranchidae (cutthroat eels)
    • Including Dysommidae, Nettodaridae, and Simenchelyidae

In some classifications the family Cyematidae of bobtail snipe eels is included in the Anguilliformes, but in the FishBase system that family is included in the order Saccopharyngiformes.

The electric eel of South America is not a true eel, but is a South American knifefish more closely related to the carps and catfishes.

Commercial species

Main commercial species
Common name Scientific name Maximum
length
Common
length
Maximum
weight
Maximum
age
Trophic level FishBase FAO ITIS IUCN status
American eel Anguilla rostrata (Lesueur, 1817) 152 cm 50 cm 7.33 kg 43 years 3.7 Not assessed
European eel Anguilla anguilla (Linnaeus, 1758) 50 cm 35 cm 6.6 kg 88 years 3.5 Critically endangered
Japanese eel Anguilla japonica Temminck & Schlegel, 1846 150 cm 40 cm 1.89 kg years 3.6 Not assessed
Short-finned eel Anguilla australis Richardson, 1841 130 cm 45 cm 7.48 kg 32 years 4.1 Not assessed

Use by humans

Freshwater eels (unagi) and marine eels (conger eel, anago) are commonly used in Japanese cuisine; foods such as unadon and unajū are popular, but expensive. Eels are also very popular in Chinese cuisine, and are prepared in many different ways. Hong Kong eel prices have often reached 1000 HKD per kg, and once exceeded 5000 HKD per kg. The European eel and other freshwater eels are eaten in Europe, the United States, and other places. A traditional east London food is jellied eels, although the demand has significantly declined since World War II. The Basque delicacy angulas consists of elver (young eels) sautéd in olive oil with garlic; elvers usually reach prices of up to 1000 euro per kg.New Zealand longfin eel is a traditional Māori food in New Zealand. In Italian cuisine, eels from the Valli di Comacchio, a swampy zone along the Adriatic coast, are especially prized, along with freshwater eels of Bolsena Lake and pond eels from Cabras, Sardinia. In northern Germany, the Netherlands, the Czech Republic, Poland, Denmark and Sweden, smoked eel is considered a delicacy.

Fishermen consumed elvers as a cheap dish, but environmental changes have reduced eel populations. They are now considered a delicacy and are priced at up to £700 per kg in the United Kingdom.[citation needed]

Eels, particularly the moray eel, are popular among marine aquarists.

Eel blood is toxic to humans and other mammals, but both cooking and the digestive process destroy the toxic protein. The toxin derived from eel blood serum was used by Charles Richet in his Nobel Prize-winning research which discovered anaphylaxis (by injecting it into dogs and observing the effect).

Eelskin leather is highly prized. It is very smooth and exceptionally strong. However, it does not come from eels. It comes from the Pacific hagfish, a jawless fish which is also known as the slime eel.

In human culture

A famous attraction on the French Polynesian island of Huahine (part of the Society Islands) is the bridge across a stream hosting 3–6-foot (0.91–1.83 m) long eels, deemed sacred by local culture.

Sustainable consumption

In 2010, Greenpeace International has added the European eel, Japanese eel and American eel to its seafood red list."The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."

Japan consumes more than 70 percent of the global eel catch.

Etymology

The English name "eel" descends from Old English ǽl, Common Germanic *ǣlaz. Also from the common Germanic are German Aal, Middle Dutch ael, Old High German âl, and Old Norse áll. Katz (1998) identifies a number of Indo-European cognates, among them the second part of the Latin word for eels, anguilla, attested in its simplex form illa (in a glossary only), and the Greek word for "eel", egkhelys (the second part of which is attested in Hesychius as elyes). The first compound member, anguis ("snake"), is cognate to other Indo-European words for "snake" (compare Old Irish escung "eel", Old High German unc "snake", Lithuanian angìs, Greek oplhis, okhis, Vedic Sanskrit áhi, Avestan aži, Armenian auj, iž, Old Church Slavonic *ǫžь, all from Proto-Indo-European *oguhis, ēguhis). The word also appears in the Old English word for "hedgehog," which is igil (meaning "snake eater"), and perhaps in the egi- of Old High German egidehsa "wall lizard". According to this theory, the name Bellerophon (Βελλεροφόντης, attested in a variant Ἐλλεροφόντης in Eustathius of Thessalonica), is also related, translating to "the slayer of the serpent" (ahihán). On this theory, the ελλερο- is an adjective form of an older word, ελλυ, meaning "snake", which is directly comparable to Hittite ellu-essar- "snake pit". This myth likely came to Greece via Anatolia. In the Hittite version of the myth, the dragon is called Illuyanka: the illuy- part is cognate to the word illa, and the -anka part is cognate to angu, a word for "snake". Since the words for "snake" (and similarly shaped animals) are often subject to taboo in many Indo-European (and non-Indo-European) languages, no unambiguous Proto-Indo-European form of the word for eel can be reconstructed. It may have been *ēl(l)-u-, *ēl(l)-o-, or something similar.

The daylight passage in the spring of elvers upstream along the Thames was at one time called "eel fare". The word 'elver' is thought to be a corruption of "eel fare."

Timeline of genera

See also

  • Eel life history

References

External links

  • Froese, Rainer, and Daniel Pauly, eds. (2006). in FishBase. January 2006 version.
  • . Integrated Taxonomic Information System. Retrieved 4 June 2008. 
  • Wikisource-logo.svg "Apodes". New International Encyclopedia. 1905.