Common names

Types of eel

8 species carry eel in an English common name. They sit in 6 families, so the group is a name, not a scientific rank.

About eel

Eels are ray-finned fish belonging to the order Anguilliformes (/ æ ŋ ˈ ɡ w ɪ l ɪ f ɔːr m iː z /), which consists of eight suborders, 20 families, 164 genera, and about 1000 species. 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), slime eels (class Myxini), 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 general rule, most eels are marine. Exceptions are the catadromous genus Anguilla and the freshwater moray, which spend most of their life in freshwater, the anadromous rice-paddy eel, which spawns in freshwater, and the freshwater snake eel Stictorhinus.

Description

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. 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. Eels swim by generating propulsive waves that travel the length of their bodies. They can swim backward by reversing the direction of the wave.

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). Most species of eels are nocturnal; they inhabit shallow waters of the ocean and burrow into sand, mud, or amongst rocks. 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.

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. Some individuals of anguillid elvers remain in brackish and marine areas close to coastlines, 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.

Gertrude Elizabeth Blood 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.

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.

Taxonomy

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.

Extant taxa

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.

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. In India, eels are popularly eaten in the Northeast. Freshwater eels, known as Kusia in Assamese, are eaten with curry, often with herbs. The European eel and other freshwater eels are mostly eaten in Europe and the United States, and is considered critically endangered. 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. 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. They became a delicacy, and the UK's most expensive species.

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.

High consumption of eels is seen in European countries leading to those eel species being considered endangered.

Sustainable consumption

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

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", ἔγχελυς enkhelys (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 *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".

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.

In culture

The ancient cathedral city of Ely in Cambridgeshire, England, derives its name from the eel. The settlement's name originates from a time when eel fishing was a vital local activity in the surrounding fenland waters.

Similarly, 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".

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.

The 2019 book The Gospel of the Eels by Patrick Svensson commented on the 'eel question' (origins of the order) and its cultural history.

Eel species in focus

These species profiles show how members of the group differ. Their biology describes each named species, rather than every fish in the group.

American Eel

The American eel (Anguilla rostrata) is a facultative catadromous eel 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.

The eel lives in fresh water and estuaries and only leaves these habitats to enter the Atlantic Ocean to make its spawning migration to the Sargasso Sea. Spawning takes place far offshore, where the eggs hatch. The female can lay up to 4 million buoyant eggs and dies after egg-laying. After the eggs hatch and the early-stage larvae develop into leptocephali, the young eels move toward North America, where they metamorphose into glass eels and enter freshwater systems where they grow as yellow eels until they begin to mature.

Description

American eels can grow to 1.22 m (4.0 ft) in length and to 7.5 kg (17 lb) in weight. Females are generally larger than males, lighter in color, with smaller eyes and higher fins. The body is elongate and snake-like. Its dorsal and anal fins are confluent with the rudimentary caudal fin. It lacks ventral fins but pectoral fins are present. The lateral line is well-developed and complete. The head is long and conical, with rather small, well-developed eyes. The mouth is terminal with jaws that are not particularly elongated. The teeth are small, pectinate or setiform in several series on the jaws and the vomer. Minute teeth also present on the pharyngeal bones, forming a patch on the upper pharyngeals. Tongue present with thick lips that are attached by a frenum in front. Nostrils are superior and well separated. Gill openings are partly below pectoral fins, relatively well-developed and well separated from one another. Inner gill slits are wide.

The scales are small, rudimentary, cycloid, relatively well embedded below the epidermis and therefore often difficult to see without magnification. The scales are not arranged in overlapping rows as they often are in other fish species but are rather irregular, in some places distributed like "parquet flooring". In general, one row of scales lies at right angle to the next, although the rows immediately above and below the lateral line lie at an angle of approximately 45°. Unlike other bony fishes, the first scales do not develop immediately after the larval stage but appear much later on.

Geographic range

The distribution of the American eel encompasses all accessible freshwater (streams and lakes), estuaries and coastal marine waters across a latitudinal range of 5 to 62 N. Their natural range includes the western North Atlantic Ocean coastline from Venezuela to Greenland and including Iceland. Inland, this species extends into the Great Lakes and the Mississippi River and its tributaries as far upstream as Minnesota and Wisconsin.

Nonindigenous occurrences of this species in the United States were recorded from Lake Mead on the Colorado River and on the Arizona border. It was stocked on a few occasions in Sacramento and San Francisco Bay, California, in the late 1800s. No apparent evidence of survival on these occasions was noted. It was also stocked and unintentionally introduced in various states, including Illinois, Indiana, Nebraska, Nevada, North Carolina, Ohio and Pennsylvania. Stockings of this species also occurred in Utah in the late 1800s, but soon disappeared.

Natural habitat

Eels are bottom dwellers. They hide in burrows, tubes, snags, masses of plants, other types of shelters. They are found in a variety of habitats including streams, rivers, and muddy or silt-bottomed lakes during their freshwater stage, as well as oceanic waters, coastal bays and estuaries. Individuals during the continental stage occasionally migrate between fresh, salt and brackish water habitats and have varying degrees of residence time in each. During winter, eels burrow under the mud and enter a state of torpor at temperatures below 5 °C (41 °F), although they may occasionally be active during this period.

American eels move from freshwater to estuaries and coastal bays to feed during spring, then either a return during the fall to overwinter (juvenile and immature adults), or a southward migration to the spawning grounds (silver eels). Continental phase eels appear highly plastic in habitat use. Eels are extremely mobile and may access habitats that appear unavailable to them, using small watercourses or moving through wet grasses. Small eels (<100 mm total length) are able to climb and may succeed in passing over vertical barriers. Habitat availability may be reduced by factors such as habitat deterioration, barriers to upstream migration (larger eels), and barriers (i.e. turbines) to downstream migration that can result in mortality.

Read the full species guide.

Painted Moray

Gymnothorax pictus, the painted moray, paintspotted moray or peppered moray, is a moray eel. The Chamorro name of the eel is títugi.

Description

The species is pale with purplish speckles, which gather together with age. Young of the species have no spots or bars; they are pale purplish with white bellies. Its maximum length is 140 cm. The peppered moray eats small fish and crustaceans. G. pictus is similar to Gymnothorax griseus. While hunting for prey, they may be completely out of the water or may leap out of water. It is dangerous to eat because it is poisonous.

Taxonomy

The peppered moray was named and described by Solander in an unpublished manuscript. Richardson said the fish might be Muraena siderea. Richardson later proved the fish was different by pointing out the difference in coloration. When the names were published as separate species, it was unknown if they were really different species. Kuep gave the species name as Sidera pantherina. Blecker later changed it to its current name. The reason why the name is still the same is because of all three people's work.

Habitat

The peppered moray can commonly be found in tropical marine waters of the Indo-Pacific and from islands of the tropical Eastern Pacific. They can also be found in very shallow water on reef flats. Places where the species has been found include Suva Reef, the Fiji Islands, Clarion Island, and the Revillagigedo Islands.

Read the full species guide.

Speckled Worm Eel

The speckled worm-eel, Myrophis punctatus, is a member of the Ophichthidae (snake eel) family. It was described by Christian Frederik Lütken in 1852. M. punctatus have brown bodies that are lighter on the ventral side than the dorsal side. The upper body is speckled with pepper-like black spots. The snout is pointed. They grow to a maximum size of 35.3 centimetres (1 ft 1.9 in).

Habitat/Distribution

The eel's depth range is 0.4m-750m while the temperature range is 6.975°C – 27.717°C. The speckled worm eel is a benthic species. It lives in tropical marine and brackish habitats that range from seagrass beds and mangroves to offshore reefs. They are found in the Western Atlantic around the island of Bermuda and from North Carolina to Brazil and throughout the Gulf of Mexico, the West Indies, and the coast of Central America, and all through the Caribbean.

Reproduction

This species makes significant seasonal migrations. They migrate to the sea to spawn. They have leptocephalus larvae. Usually only juveniles are found inshore. They appear along the coast between December and May from drifting in from offshore spawning areas.

Other information

They are caught as baitfish along the northern Brazilian coast using ichthyotoxic plants. Locomotion type: Balistiform Lobotes surinamensis and Thunnus thynnus thynnus feed on Myrophis punctatus.

Read the full species guide.

Range