American eel, Anguilla rostrata
|See text for suborders and families.|
True eels (Anguilliformes) are an order of fish, which consists of 4 suborders, 19 families, 110 genera and 400 species. Most eels are predators.
The flat and transparent larva of the eel is called a leptocephalus. A young eel is called an elver.
Most eels prefer to dwell in shallow waters or hide at the bottom layer of the ocean, sometimes in holes. Only the Anguillidae family comes to fresh water to dwell there (not to breed). Some eels dwell in deep water (in case of family Synaphobranchidae, this comes to a depth of 4,000 m), or are active swimmers (the family Nemichthyidae - to the depth of 500 m).
Eels lack pelvic fins and the associated skeletal structures. The pectoral fins (in those species that have them) are midlateral in position and lack the posttemporal bone, which connects the shoulder girdle to the skull. The caudal and anal fins are long, usually connecting with the tail (caudal) fin. The caudal fin lacks rays or may be absent. The body is very elongated.
The number of rays of the gill webbing ranges from 6 to 51, though sometimes they are absent altogether. The scales are cycloid or absent.
Depending on their species, eels can reach from 10 cm to 3 m, and weigh up to 65 kg.
The life cycle of the eel was a mystery for a very long time, because larval eels look very different from adult eels, and were thought to be a separate species.
This classification follows FishBase in dividing the eels into fifteen families. Additional families that are included in other classifications (notably ITIS and Systema Naturae 2000) are noted below the family with which they are synomized in the FishBase system.
Suborders and families
- Anguillidae (freshwater eels)
Chlopsidae (false morays)
Moringuidae (spaghetti eels)
Muraenidae (moray eels)
- Including Macrocephenchelyidae
Derichthyidae (longneck eels)
- Including Nessorhamphidae
- Muraenesocidae (conger pikes)
Nettastomatidae (witch eels)
Ophichthidae (snake eels)
- Nemichthyidae (snipe eels)
Serrivomeridae (sawtooth eels)
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 so-called "Electric Eel" of South America is not a true eel, but is more closely related to the Carp.
Use by humans
Freshwater eels (unagi) and marine eels (Conger eel, anago) are commonly used in Japanese cuisine. Unadon is a very popular but rather expensive food. Eels are used in Cantonese and Shanghai cuisine too. The European eel and other freshwater eels are eaten in Europe, the United States, and other places around the world. A traditional East London food is jellied eels. The Basque delicacy angulas consists of deep-fried elvers.
In recent years, some cryptozoologists have theorised that the Loch Ness Monster might be a giant eel (as was the case in Steve Alten's novel The Loch, where the monster was a giant Sargasso anguilla eel).
There is an urban legend that wallets made out of electric eels will demagnetize your credit cards. This was proven to be untrue in an episode of the Mythbusters TV show. Actually, as pointed out in the Straight Dope, eel-skin wallets are made from hagfish which are unrelated to electric eels. Furthermore, it seems that magnetic clasps, not eel leather, are to blame for demagnetization.
Eel blood is toxic. The toxic protein it contains is destroyed by cooking. The toxin derived from eel blood serum was used by Charles Robert Richet in his Nobel winning research which discovered anaphylaxis (by injecting it into dogs and observing the effect).
On January 31, 1930, the Danish research ship; "The Dana", captured, (south of Africa's Cape of Good Hope), what they thought at the time was a six-feet long eel larva. This could have meant there were very long eels in the sea, since the typical eel larva is three inches long, while the adults can grow from about 4 feet to 16 feet long. In 1970, Dr. David G. Smith from the University of Miami, identified the larva found as that of the spiny eel, an eel-like fish whose larvae length is equal to its adult length, while the larvae length of the true eel is much shorter than its adult length. 
In Micronesia, eels are believed to hold the souls of one's departed relatives. As such, killing eels is a grave offence and was once punishable by death.
- "Anguilliformes". FishBase. Ed. Ranier Froese and Daniel Pauly. January 2006 version. N.p.: FishBase, 2006.