Temporal range: Cretaceous–Recent 
|American eel, Anguilla rostrata|
L. S. Berg, 1943
An eel is any fish belonging to the order Anguilliformes (//), which consists of four suborders, 20 families, 111 genera and about 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.
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 g (1.1 oz) to well over 25 kg (55 lb). They possess no pelvic fins, and many species also lack pectoral fins. The dorsal and anal fins are fused with the caudal 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, 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 regularly inhabit fresh water, but they, too, return to the sea to breed.
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).
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.
This classification follows FishBase in dividing the eels into 20 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.
Suborders and families
- Anguillidae (freshwater eels)
- Chlopsidae (false morays)
- Heterenchelyidae (mud eels)
- Moringuidae (spaghetti eels)
- Muraenidae (moray eels)
- Myrocongridae (thin eels)
- Colocongridae (worm eels)
- Congridae (congers)
- Including Macrocephenchelyidae
- Including Nessorhamphidae
- Muraenesocidae (pike congers)
- Nettastomatidae (duckbill eels)
- Ophichthidae (snake eels)
- Including Dysommidae, Nettodaridae, and Simenchelyidae
|Main commercial species|
|Common name||Scientific name||Maximum
|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)||150 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||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 (128.86 US Dollars) 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) sautéed 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.
Elvers, often fried, used to be a cheap dish in the United Kingdom; but, as across Europe, their numbers collapsed during the 1990s. They are now not just a delicacy, but the UK's most expensive species.
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
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 ophis, 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.
Timeline of genera
- Froese, Rainer, and Daniel Pauly, eds. (2009). "Anguilliformes" in FishBase. January 2009 version.
- McCosker, John F. (1998). Paxton, J.R. & Eschmeyer, W.N., ed. Encyclopedia of Fishes. San Diego: Academic Press. pp. 86–90. ISBN 0-12-547665-5.
- Prosek, James (2010). Eels: An Exploration. New York: HarperCollins. ISBN 978-0-06-056611-1.
- Conger conger, European conger: fisheries, gamefish, aquarium. Fishbase.org
- FishBase. FishBase (2011-11-15).
- Campbell, Lady Colin (1886). A Book of the Running Brook: and of Still Waters. New York: O. Judd Co. pp. 9; 18.
- Inoue, Jun G. et al. (2010). "Deep-ocean origin of the freshwater eels". Biol. Lett. 6 (3): 363–366. doi:10.1098/rsbl.2009.0989. PMC 2880065. PMID 20053660.
- Froese, Rainer and Pauly, Daniel, eds. (2012). "Anguilla rostrata" in FishBase. May 2012 version.
- "Anguilla rostrata". Integrated Taxonomic Information System. Retrieved May 2015.
- Froese, Rainer and Pauly, Daniel, eds. (2012). "Anguilla anguilla" in FishBase. May 2012 version.
- Anguilla anguilla (Linnaeus, 1758) FAO, Species Fact Sheet. Retrieved 20 May 2012.
- "Anguilla anguilla". Integrated Taxonomic Information System. Retrieved May 2012.
- Freyhof, J and Kottelat M (2010). "Anguilla anguilla". IUCN Red List of Threatened Species. Version 2011.2. International Union for Conservation of Nature. Retrieved 20 May 2012.
- Froese, Rainer and Pauly, Daniel, eds. (2012). "Anguilla japonica" in FishBase. May 2012 version.
- Anguilla japonica, Temminck & Schlegel, 1846 FAO, Species Fact Sheet. Retrieved May 2012.
- "Anguilla japonica". Integrated Taxonomic Information System. Retrieved May 2012.
- Froese, Rainer and Pauly, Daniel, eds. (2012). "Anguilla australis" in FishBase. May 2012 version.
- "Anguilla australis". Integrated Taxonomic Information System. Retrieved May 2012.
- Champken, Neil (2 June 2006). "Would you pay £600 for a handful of baby eels?". theguardian.com. Retrieved 7 April 2015.
- Leake, Jonathan (7 February 2015). "EU's eel edict costs UK £100m". The Sunday Times. Retrieved 7 April 2015.
- "Poison in the Blood of the Eel", New York Times, 9 April 1899, viewed at , accessed 22 January 2010
- "The plight of the eel", BBC online, as seen at , accessed 22 January 2010, mentions that "Only 0.1 ml/kg is enough to kill small mammals, such as a rabbit..."
- "Blood serum of the eel." M. Sato. Nippon Biseibutsugakukai Zasshi (1917), 5 (No. 35), From: Abstracts Bact. 1, 474 (1917)
- "Hemolytic and toxic properties of certain serums." Wm. J. Keffer, Albert E. Welsh. Mendel Bulletin (1936), 8 76-80.
- http://www.snopes.com/science/eelskin.asp retrieved 21 April 2010
- Barss, William (1993), "Pacific hagfish, Eptatretus stouti, and black hagfish, E. deani: the Oregon Fishery and Port sampling observations, 1988-92", Marine Fisheries Review (Fall, 1993), retrieved 21 April 2010
- Greenpeace International Seafood Red list
- "Indonesia eel hot item for smugglers". The Japan Times. Retrieved 30 July 2013.
- Katz, J. (1998). "How to be a Dragon in Indo-European: Hittite illuyankas and its Linguistic and Cultural Congeners in Latin, Greek, and Germanic". In Jasanoff; Melchert; Oliver. Mír Curad. Studies in Honor of Calvert Watkins. Innsbruck. pp. 317–334. ISBN 3-85124-667-5.