Eels
Temporal range:
Anguilla japonica
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Superorder: Elopomorpha
Order: Anguilliformes
L. S. Berg, 1943
Type genus
Anguilla
Suborders
Protanguilloidei
Synaphobranchoidei
Muraenoidei
Chlopsoidei
Congroidei
Moringuoidei
Saccopharyngoidei
Anguilloidei

Eels are ray-finned fish belonging to the order Anguilliformes (/æŋˈɡwɪlɪfɔːrmiːz/), which consists of eight suborders, 20 families, 164 genera, and about 1000 species.[3][4] Eels undergo considerable development from the early larval stage to the eventual adult stage and are usually predators.

The term "eel" is also used for some other eel-shaped fish, such as electric eels (genus Electrophorus), spiny eels (family Mastacembelidae), swamp eels (family Synbranchidae), and deep-sea spiny eels (family Notacanthidae). However, these other clades evolved their eel-like shapes independently from the true eels. As a main rule, most eels are marine. Exceptions are the catadromous genus Anguilla and the freshwater moray,[5] which spend most of their life in freshwater, the anadromous rice-paddy eel, which spawns in freshwater, and the freshwater snake eel Stictorhinus.[6]

Description

The European conger is the heaviest of all eels.

Eels are elongated fish, ranging in length from 5 cm (2 in) in the one-jawed eel (Monognathus ahlstromi) to 4 m (13 ft) in the slender giant moray.[7] Adults range in weight from 30 g (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.[1] Eels swim by generating waves that travel the length of their bodies. They can swim backward by reversing the direction of the wave.[8]

Most eels live in the shallow waters of the ocean and burrow into sand, mud, or amongst rocks. Most eel species are nocturnal, and thus are rarely seen. Sometimes, they are seen living together in holes or "eel pits". Some 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.[9]

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).[10] Other eels are longer, but do not weigh as much, such as the slender giant moray, which reaches 4 m (13 ft).[11]

Life cycle

Eels begin life as flat and transparent larvae, called leptocephali. Eel larvae drift in the sea's surface waters, feeding on marine snow, small particles that float in the water. Eel larvae then metamorphose into glass eels and become elvers before finally seeking out their juvenile and adult habitats.[7] Some individuals of anguillid elvers remains in brackish and marine areas close to coastlines,[12] but most of them enter freshwater where they travel upstream and are forced to climb up obstructions, such as weirs, dam walls, and natural waterfalls.

Life cycle of a typical (catadromous) eel

Lady Colin Campbell found that the eel fisheries at Ballisodare were greatly improved by the hanging of loosely plaited grass ladders over barriers, enabling elvers to ascend more easily.[13]

Classification

Several sets of classifications of eels exist; some, such as FishBase which divide eels into 20 families, whereas other classification systems such as ITIS and Systema Naturae 2000 include additional eel families, which are noted below.

Genomic studies indicate that there is a monophyletic group that originated among the deep-sea eels.[14]

Suborders and families

Taxonomy based on Nelson, Grande and Wilson 2016.[15]

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.

Phylogeny

Phylogeny based on Johnson et al. 2012.[16]

Anguilliformes
Protanguilloidei

Protanguillidae

Synaphobranchoidei

Synaphobranchidae

Muraenoidei

Heterenchelyidae

Myrocongridae

Muraenidae

Chlopsoidei

Chlopsidae

Congroidei

Derichthyidae

Nettastomatidae

Congridae

Ophichthidae

Muraenesocidae

Moringuoidei

Moringuidae

Saccopharyngoidei

Eurypharyngidae

Saccopharyngidae

Monognathidae

Cyematidae

Anguilloidei

Nemichthyidae

Serrivomeridae

Anguillidae

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 [17] [18] EN IUCN 3 1.svg
Endangered[19]
European eel Anguilla anguilla (Linnaeus, 1758) 150 cm 35 cm 6.6 kg 88 years 3.5 [20] [21] [22] CR IUCN 3 1.svg
Critically endangered[23]
Japanese eel Anguilla japonica Temminck & Schlegel, 1846 150 cm 40 cm 1.89 kg 3.6 [24] [25] [26] EN IUCN 3 1.svg
Endangered[27]
Short-finned eel Anguilla australis Richardson, 1841 130 cm 45 cm 7.48 kg 32 years 4.1 [28] [29] EN IUCN 3 1.svg
Near Threatened[30]

Use by humans

Eel picker in Maasholm, sculpture by Bernd Maro
Green water culture system for Japanese eel
Positioning eel traps in Inle Lake (Myanmar)

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. In India, eels are popularly eaten in the Northeast. Freshwater eels, known as Kusia in Assamese, are eaten with curry,[31] often with herbs.[32] The European eel and other freshwater eels are mostly eaten in Europe and the United States, and is considered critically endangered.[33] A traditional east London food is jellied eels, although the demand has significantly declined since World War II. The Spanish cuisine delicacy angulas consists of elver (young eels) sautéed in olive oil with garlic; elvers usually reach prices of up to 1000 euro per kg.[34] 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, were once a cheap dish in the United Kingdom. During the 1990s, their numbers collapsed across Europe.[35] They became a delicacy, and the UK's most expensive species.[36]

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

Eel blood is toxic to humans[37] and other mammals,[38][39][40] but both cooking and the digestive process destroy the toxic protein. The toxin derived from eel blood serum was used by Charles Robert Richet in his Nobel Prize-winning research which discovered anaphylaxis (by injecting it into dogs and observing the effect). The poison used by Richet was actually obtained from sea anemones.[41]

Eelskin leather is highly prized. It is very smooth and exceptionally strong. It does not actually come from eels, but rather from the Pacific hagfish, a jawless fish which is also known as the slime eel.[42][43]

In culture

The large lake of Almere, which existed in the early Medieval Netherlands, got its name from the eels which lived in its water (the Dutch word for eel is aal or ael, so: "ael mere" = "eel lake"). The name is preserved in the new city of Almere in Flevoland, given in 1984 in memory of this body of water on whose site the town is located.

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".[13]

A famous attraction on the French Polynesian island of Huahine (part of the Society Islands) is the bridge across a stream hosting three- to six-foot-long eels, deemed sacred by local culture.

Eel fishing in Nazi-era Danzig plays an important role in Günter Grass' novel The Tin Drum. The cruelty of humans to eels is used as a metaphor for Nazi atrocities, and the sight of eels being killed by a fisherman triggers the madness of the protagonist's mother.

Sinister implications of eels fishing are also referenced in Jo Nesbø's Cockroaches, the second book of the Harry Hole detective series. The book's background includes a Norwegian village where eels in the nearby sea are rumored to feed on the corpses of drowned humans, making the eating of these eels verge on cannibalism.

Sustainable consumption

In 2010, Greenpeace International added the European eel, Japanese eel, and American eel to its seafood red list.[44] Japan consumes more than 70% of the global eel catch.[45]

Etymology

The English name "eel" descends from Old English ǣl, Common Germanic *ēlaz. Also from the common Germanic are West Frisian iel, Dutch aal, German Aal, and Icelandic 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).[46] 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 *h₁ogʷʰis). 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".[47][48]

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). In 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

See also

References

  1. 1 2 Froese, Rainer, and Daniel Pauly, eds. (2009). "Anguilliformes" in FishBase. January 2009 version.
  2. ↑ Pl. 661 in Garsault, F. A. P. de 1764. Les figures des plantes et animaux d'usage en medecine, décrits dans la Matiere Medicale de Mr. Geoffroy medecin, dessinés d'après nature par Mr. de Gasault, gravés par Mrs. Defehrt, Prevost, Duflos, Martinet &c. Niquet scrip. [5]. - pp. [1-4], index [1-20], Pl. 644–729. Paris.
  3. ↑ "WoRMS - World Register of Marine Species - Anguilliformes". www.marinespecies.org.
  4. ↑ "WoRMS - World Register of Marine Species - Saccopharyngiformes". www.marinespecies.org.
  5. ↑ Ebner, Brendan C.; Donaldson, James A.; Courtney, Robert; Fitzpatrick, Richard; Starrs, Danswell; Fletcher, Cameron S.; Seymour, Jamie (23 September 2019). "Averting danger under the bridge: video confirms that adult small-toothed morays tolerate salinity before and during tidal influx". Pacific Conservation Biology. 26 (2): 182–189. doi:10.1071/PC19023 – via www.publish.csiro.au.
  6. ↑ "Family OPHICHTHIDAE" (PDF).
  7. 1 2 McCosker, John F. (1998). Paxton, J.R.; Eschmeyer, W.N. (eds.). Encyclopedia of Fishes. San Diego: Academic Press. pp. 86–90. ISBN 0-12-547665-5.
  8. ↑ Long Jr, J. H., Shepherd, W., & Root, R. G. (Loot). Manueuverability and reversible propulsion: How eel-like fish swim forward and backward using travelling body waves". In: Proc. Special Session on Bio-Engineering Research Related to Autonomous Underwater Vehicles, 10th Int. Symp. (pp. 118–134).
  9. ↑ Prosek, James (2010). Eels: An Exploration. New York: HarperCollins. ISBN 978-0-06-056611-1.
  10. ↑ Conger conger, European conger: fisheries, gamefish, aquarium. Fishbase.org
  11. ↑ FishBase Archived 10 November 2013 at the Wayback Machine. FishBase (15 November 2011).
  12. ↑ Arai, Takaomi (1 October 2020). "Ecology and evolution of migration in the freshwater eels of the genus Anguilla Schrank, 1798". Heliyon. 6 (10): e05176. doi:10.1016/j.heliyon.2020.e05176. PMC 7553983 – via ScienceDirect.
  13. 1 2 Campbell, Lady Colin (1886). A Book of the Running Brook: and of Still Waters. New York: O. Judd Co. pp. 9, 18.
  14. ↑ 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.
  15. ↑ Nelson, Joseph S.; Grande, Terry C.; Wilson, Mark V. H. (2016). Fishes of the World (5th ed.). John Wiley & Sons. ISBN 9781118342336.
  16. ↑ Johnson, G. D.; Ida H.; Sakaue J.; Sado T.; Asahida T.; Miya M. (2012). "A 'living fossil' eel (Anguilliformes: Protanguillidae, fam nov) from an undersea cave in Palau". Proceedings of the Royal Society. (in press) (1730): 934–943. doi:10.1098/rspb.2011.1289. PMC 3259923. PMID 21849321.Open access icon
  17. ↑ Froese, Rainer; Pauly, Daniel (eds.) (2012). "Anguilla rostrata" in FishBase. May 2012 version.
  18. ↑ "Anguilla rostrata". Integrated Taxonomic Information System. Retrieved 20 May 2015.
  19. ↑ Jacoby, D.; Casselman, J.; DeLucia, M.; Gollock, M. (2017) [amended version of 2014 assessment]. "Anguilla rostrata". IUCN Red List of Threatened Species. 2017: e.T191108A121739077. doi:10.2305/IUCN.UK.2017-3.RLTS.T191108A121739077.en. Retrieved 12 November 2021.
  20. ↑ Froese, Rainer; Pauly, Daniel (eds.) (2012). "Anguilla anguilla" in FishBase. May 2012 version.
  21. ↑ Anguilla anguilla (Linnaeus, 1758) FAO, Species Fact Sheet. Retrieved 20 May 2012.
  22. ↑ "Anguilla anguilla". Integrated Taxonomic Information System. Retrieved 20 May 2012.
  23. ↑ Pike, C.; Crook, V.; Gollock, M. (2020). "Anguilla anguilla". IUCN Red List of Threatened Species. 2020: e.T60344A152845178. doi:10.2305/IUCN.UK.2020-2.RLTS.T60344A152845178.en. Retrieved 12 November 2021.
  24. ↑ Froese, Rainer; Pauly, Daniel (eds.) (2012). "Anguilla japonica" in FishBase. May 2012 version.
  25. ↑ Anguilla japonica, Temminck & Schlegel, 1846 FAO, Species Fact Sheet. Retrieved May 2012.
  26. ↑ "Anguilla japonica". Integrated Taxonomic Information System. Retrieved 20 May 2012.
  27. ↑ Jacoby, D. & Gollock, M. (2014). "Anguilla japonica". IUCN Red List of Threatened Species. 2014: e.T166184A1117791. doi:10.2305/IUCN.UK.2014-1.RLTS.T166184A1117791.en. Retrieved 4 January 2018.
  28. ↑ Froese, Rainer; Pauly, Daniel (eds.) (2012). "Anguilla australis" in FishBase. May 2012 version.
  29. ↑ "Anguilla australis". Integrated Taxonomic Information System. Retrieved 20 May 2012.
  30. ↑ Pike, C.; Crook, V.; Gollock, M. (2019) [errata version of 2019 assessment]. "Anguilla australis". IUCN Red List of Threatened Species. 2019: e.T195502A154801652. doi:10.2305/IUCN.UK.2019-2.RLTS.T195502A154801652.en. Retrieved 12 November 2021.
  31. ↑ "Swamp Eels". Encyclopedia of Life. Retrieved 24 June 2022.
  32. ↑ Bhuyan, Avantika (30 March 2018). "The little fish in big rivers". The Live Mint. Retrieved 24 June 2022.
  33. ↑ Acou, Anthony, et al. "Assessment of the Quality of European Silver Eels and Tentative Approach to Trace the Origin of Contaminants – A European Overview." The science of the total environment. 743 (2020): n. pag. Web.
  34. ↑ "Buber's Basque Page: Angulas".
  35. ↑ Champken, Neil (2 June 2006). "Would you pay £600 for a handful of baby eels?". theguardian.com. Retrieved 7 April 2015.
  36. ↑ Leake, Jonathan (7 February 2015). "EU's eel edict costs UK £100m". The Sunday Times. Archived from the original on 10 July 2015. Retrieved 7 April 2015.
  37. ↑ "Poison in the Blood of the Eel" (PDF). 9 April 1899. Retrieved 22 January 2010.
  38. ↑ "The plight of the eel (mentions that "Only 0.1 ml/kg is enough to kill small mammals, such as a rabbit..." BBC online. Retrieved 22 January 2010.
  39. ↑ "Blood serum of the eel." M. Sato. Nippon Biseibutsugakukai Zasshi (1917), 5 (No. 35), From: Abstracts Bact. 1, 474 (1917)
  40. ↑ "Hemolytic and toxic properties of certain serums." Wm. J. Keffer, Albert E. Welsh. Mendel Bulletin (1936), 8 76–80.
  41. ↑ "Charles Robert Richet". encyclopedia.com.
  42. ↑ snopes (4 December 2015). "Eelskin Demagnitizes : snopes.com". Snopes. Retrieved 21 April 2010.
  43. ↑ 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), archived from the original on 7 March 2012, retrieved 21 April 2010
  44. ↑ "Greenpeace Seafood Red list". Greenpeace International.
  45. ↑ "Indonesia eel hot item for smugglers". The Japan Times. 29 July 2013. Retrieved 30 July 2013.
  46. ↑ 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 (eds.). Mír Curad. Studies in Honor of Calvert Watkins. Innsbruck. pp. 317–334. ISBN 3-85124-667-5.{{cite book}}: CS1 maint: location missing publisher (link)
  47. ↑ Arai, Takaomi (22 February 2016). Biology and Ecology of Anguillid Eels. CRC Press. ISBN 978-1-4822-5516-4.
  48. ↑ Ross, Stephen T.; Brenneman, William Max (2001). The Inland Fishes of Mississippi. Univ. Press of Mississippi. ISBN 978-1-57806-246-1.


Further references

  • Tesch FW and White RJ (2008). The Eel. John Wiley & Sons. ISBN 9781405173438.
  • Patrik Svensson (2019). The Book of Eels, English translation (2020) by Agnes Broomé, published by ecco, ISBN 9780062968814.
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