Eels (Anguilliformes) are an order of fish that consists of four suborders, 20 families, 111 genera and about 800 different species. Most are predators. The term “eel” is also used for some other similarly shaped fish, such as the electric and spiny eels. These are however not members of the Anguilliformes order.
Eels are elongated fish, ranging in length from 5 cm (2″) in the one-jawed eel to 4 m (13 ft) in the slender giant moray. They posses no pelvic fins with most species also lacking pectoral fins. The dorsal and anal fins are fused with the caudal fin, forming a single ribbon running along much of the animal’s length.
Most live in shallow ocean waters and burrow into sand, mud or among rocks. They are rarely seen because many species are nocturnal. Sometimes they live together in holes, or “eel pits”. Some of them also live in the deeper water on the continental shelves as deep as 4,000 meters (13,000 ft). Only members of the Anguilla family regularly inhabit fresh water, but they too, return to the sea to breed.