The European eel, Anguilla anguilla, is a species of eel, a snake-like, catadromous fish. They can reach in exceptional cases a length of 1½ m, but are normally much smaller, about 60–80 cm, and rarely more than 1 m.
Much of the European eel’s life history was a mystery for centuries, as fishermen never caught anything they could identify as a young eel. Research in the 19th and 20th centuries shed some light on the subject, though questions remain.
They are generally believed to spawn in the Sargasso Sea, after which the adult eels die. The larvae (Leptocephalus) drift towards Europe in a three-hundred-day migration (FAO data). When approaching the European coast the larvae metamorphose into a transparent larval stage called "glass eel", and enter estuaries and start migrating upstream.
After entering fresh water, the glass eels metamorphose into elvers, miniature versions of the adult eels. As the eel grows it becomes known as a "yellow eel" due to the brownish-yellow color of their sides and belly. After 5 - 20 years in freshwater the eels become sexually mature, their eyes grow larger, their flanks become silver and belly white in color. In this stage the eels are known as "silver eels", and they begin their migration back to the Sargasso sea to spawn