The common eel is long and snake-like in shape with a tough, slimy skin. The dorsal fin starts on the back some way behind the gill slits and small pectoral fins and runs the length of the body. At the tail the dorsal fin merges with the ventral fin, that runs along the underside of the body. The eel can be black, brown or dark olive green in colour above, paler and yellowish on the underside. Sexually maturing eels become silver rather than yellow.Anguilla anguilla
has a complex life history that is poorly understood. It involves migration of mature adults from European rivers and estuaries to the Sargasso Sea in the west Atlantic for spawning, and the subsequent return of juveniles. They metamorphose twice, part of the life cycle spent in fresh water and part in estuarine or full sea water (Whitehead et al.,
1986). The adult eels and the returning juveniles (elvers) are commercially fished. The common eel has small eyes and its lower jaw projects from the upper, which distinguishes it from the conger eel, Conger conger
. In the common eel the dorsal fin arises about a head's length behind the gill slits and pectoral fins while in the conger eel the fin arises further forward, from just behind the pectoral fins.