Eels Temporal range: | |
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Anguilla japonica | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Actinopterygii |
Superorder: | Elopomorpha |
Order: | Anguilliformes L. S. Berg, 1943 |
Type genus | |
Anguilla | |
Suborders | |
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), swamp eels (order Synbranchiformes), and deep-sea spiny eels (family Notacanthidae). However, these other clades, with the exception of deep-sea spiny eels, whose order Notacanthiformes is the sister clade to true eels, 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]
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]
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.
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]
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Commercial fish |
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Large pelagic |
Forage |
Demersal |
Mixed |
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]
The earliest fossil eels are known from the Late Cretaceous (Cenomanian) of Lebanon. These early eels retain primitive traits such as pelvic fins and thus do not appear to be closely related to any extant taxa. Body fossils of modern eels do not appear until the Eocene, although otoliths assignable to extant eel families and even some genera have been recovered from the Campanian and Maastrichtian, indicating some level of diversification among the extant groups prior to the Cretaceous-Paleogene extinction, which is also supported by phylogenetic divergence estimates. One of these otolith taxa, the mud-dwelling Pythonichthys arkansasensis , appears to have thrived in the aftermath of the K-Pg extinction, based on its abundance. [15] [16] [17]
Taxonomy based on Nelson, Grande and Wilson 2016. [18]
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 based on Johnson et al. 2012. [19]
Anguilliformes |
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Based on the Paleobiology Database: [20] [21]
Main commercial species | ||||||||||
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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 | [22] | [23] | Endangered [24] | |
European eel | Anguilla anguilla(Linnaeus, 1758) | 150 cm | 35 cm | 6.6 kg | 88 years | 3.5 | [25] | [26] | [27] | Critically endangered [28] |
Japanese eel | Anguilla japonicaTemminck & Schlegel, 1846 | 150 cm | 40 cm | 1.89 kg | 3.6 | [29] | [30] | [31] | Endangered [32] | |
Short-finned eel | Anguilla australisRichardson, 1841 | 130 cm | 45 cm | 7.48 kg | 32 years | 4.1 | [33] | [34] | Near Threatened [35] |
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.[ citation needed ] Freshwater eels, known as Kusia in Assamese, are eaten with curry, [36] often with herbs. [37] The European eel and other freshwater eels are mostly eaten in Europe and the United States, and is considered critically endangered. [38] 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. [39] 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. [40] They became a delicacy, and the UK's most expensive species. [41]
Eels, particularly the moray eel, are popular among marine aquarists.
Eel blood is toxic to humans [42] and other mammals, [43] [44] [45] 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).[ citation needed ] The poison used by Richet was actually obtained from sea anemones. [46]
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. [47] [48]
High consumption of eels is seen in European countries leading to those eel species being considered endangered.
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.
In 2010, Greenpeace International added the European eel, Japanese eel, and American eel to its seafood red list. [49] Japan consumes more than 70% of the global eel catch. [50]
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). [51] 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". [52] [53]
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.
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The European eel is a species of eel. They are critically endangered due to overfishing by fisheries on coasts for human consumption and parasites.
The American eel is a facultative catadromous fish found on the eastern coast of North America. Freshwater eels are fish belonging to the elopomorph superorder, a group of phylogenetically ancient teleosts. The American eel has a slender, supple, snake-like body that is covered with a mucus layer, which makes the eel appear to be naked and slimy despite the presence of minute scales. A long dorsal fin runs from the middle of the back and is continuous with a similar ventral fin. Pelvic fins are absent, and relatively small pectoral fins can be found near the midline, followed by the head and gill covers. Variations exist in coloration, from olive green, brown shading to greenish-yellow and light gray or white on the belly. Eels from clear water are often lighter than those from dark, tannic acid streams.
Eels are any of several long, thin, bony fishes of the order Anguilliformes. They have a catadromous life cycle, that is: at different stages of development migrating between inland waterways and the deep ocean. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel is a mystery which has covered a long period of scientific history into the present day. Of significant interest is the search for the spawning grounds for the various species of eels and identifying impacts to population decline in each stage of the life cycle.
The short-finned eel, also known as the shortfin eel, is one of the 15 species of eel in the family Anguillidae. It is native to the lakes, dams and coastal rivers of south-eastern Australia, New Zealand, and much of the South Pacific, including New Caledonia, Norfolk Island, Lord Howe Island, Tahiti, and Fiji.
Moray eels, or Muraenidae, are a family of eels whose members are found worldwide. There are approximately 200 species in 15 genera which are almost exclusively marine, but several species are regularly seen in brackish water, and a few are found in fresh water.
The Anguillidae are a family of ray-finned fish that contains the freshwater eels. Except from the genus Neoanguilla, with the only known species Neoanguilla nepalensis from Nepal, all the extant species and six subspecies in this family are in the genus Anguilla, and are elongated fish of snake-like bodies, with long dorsal, caudal and anal fins forming a continuous fringe. They are catadromous, spending their adult lives in freshwater, but migrating to the ocean to spawn.
The superorder Elopomorpha contains a variety of types of fishes that range from typical silvery-colored species, such as the tarpons and ladyfishes of the Elopiformes and the bonefishes of the Albuliformes, to the long and slender, smooth-bodied eels of the Anguilliformes. The one characteristic uniting this group of fishes is they all have leptocephalus larvae, which are unique to the Elopomorpha. No other fishes have this type of larvae.
Muraena is a genus of twelve species of large eels in the family Muraenidae.
The New Zealand longfin eel, also known as ōrea, is a species of freshwater eel that is endemic to New Zealand. It is the largest freshwater eel in New Zealand and the only endemic species – the other eels found in New Zealand are the native shortfin eel, also found in Australia, and the naturally introduced Australian longfin eel. Longfin eels are long-lived, migrating to the Pacific Ocean near Tonga to breed at the end of their lives. They are good climbers as juveniles and so are found in streams and lakes a long way inland. An important traditional food source for Māori, who name them ōrea, longfin eel numbers are declining and they are classified as endangered, but over one hundred tonnes are still commercially fished each year.
The speckled longfin eel, Australian long-finned eel or marbled eel is one of 15 species of eel in the family Anguillidae. It has a long snake-like cylindrical body with its dorsal, tail and anal fins joined to form one long fin. It usually has a brownish green or olive green back and sides with small darker spots or blotches all over its body. Its underside is paler. It has a small gill opening on each side of its wide head, with thick lips. It is Australia's largest freshwater eel, and the female usually grows much larger than the male. It is also known as the spotted eel.
The Anguilloidei are a suborder of the order Anguilliformes containing three families:
Anguilla bicolor is a species of eel in the genus Anguilla of the family Anguillidae, consisting of two subspecies.
The mottled eel, also known as the African mottled eel, the Indian longfin eel, the Indian mottled eel, the long-finned eel or the river eel, is a demersal, catadromous eel in the family Anguillidae. It was described by John McClelland in 1844. It is a tropical, freshwater eel which is known from East Africa, Bangladesh, Andaman Islands, Mozambique, Malawi, Sri Lanka, Sumatra, and Indonesia and recently from Madagascar. The eels spend most of their lives in freshwater at a depth range of 3–10 metres, but migrate to the Indian Ocean to breed. Males can reach a maximum total length of 121 centimetres and a maximum weight of 7,000 grams. The eels feed primarily off of benthic crustaceans, mollusks, finfish and worms.
Gymnothorax is a genus of fish in the family Muraenidae found in Atlantic, Indian and Pacific Ocean. With more than 120 species, it the most speciose genus of moray eels.
The giant mottled eel, also known as the marbled eel, is a species of tropical anguillid eel that is found in the Indo-Pacific and adjacent freshwater habitats.
The European conger is a species of conger of the family Congridae. It is the heaviest eel in the world and native to the northeast Atlantic, including the Mediterranean Sea.
Eels are elongated fish, ranging in length from five centimetres (2 in) to four metres (13 ft). Adults range in weight from 30 grams to over 25 kilograms. 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 live in deeper water on the continental shelves and over the slopes deep as 4,000 metres (13,000 ft). Only members of the family Anguillidae regularly inhabit fresh water, but they too return to the sea to breed.
The Pacific shortfinned eel, also known as the Pacific shortfinned freshwater eel, the short-finned eel, and the South Pacific eel, is an eel in the family Anguillidae. It was described by Albert Günther in 1871. It is a tropical, freshwater eel which is known from western New Guinea, Queensland, Australia, the Society Islands, and possibly South Africa. The eels spend most of their lives in freshwater, but migrate to the Pacific Ocean to breed. Males can reach a maximum total length of 110 centimetres, but more commonly reach a TL of around 60 cm. The Pacific shortfinned eel is most similar to Anguilla australis, and Anguilla bicolor, but can be distinguished by the number of vertebrae.
Fish go through various life stages between fertilization and adulthood. The life of fish start as spawned eggs which hatch into immotile larvae. These larval hatchlings are not yet capable of feeding themselves and carry a yolk sac which provides stored nutrition. Before the yolk sac completely disappears, the young fish must mature enough to be able to forage independently. When they have developed to the point where they are capable of feeding by themselves, the fish are called fry. When, in addition, they have developed scales and working fins, the transition to a juvenile fish is complete and it is called a fingerling, so called as they are typically about the size of human fingers. The juvenile stage lasts until the fish is fully grown, sexually mature and interacting with other adult fish.
Bathycongrus aequoreus is an eel in the family Congridae. It was described by Charles Henry Gilbert and Frank Cramer in 1897, originally under the genus Congermuraena. It is a marine, deep water-dwelling eel which is known from Hawaii, in the eastern central Pacific Ocean. It dwells at a depth range of 300–686 metres, prefers deeper water and leads a benthic lifestyle.
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