The European Eel is a migratory fish that spawns somewhere in or near the Sargasso Sea. The eggs hatch and drift on the gulf stream to Europe as a willow leaf shaped  larvae called Leptocephalus. When they reach our continental shelf they Metamorphosise into glass eels, enter our rivers , change to yellow elvers and live  to adulthood between 7-80 years before changing into a silver eel and returning the 4-5000 miles back to the Sargasso sea to spawn. They are a catadromous fish, a panmictic species, that has fascinated us for centuries.