European Eel

The European eel, Anguilla anguilla, is a species of eel, a snake-like, facultatively catadromous fish. They can reach in exceptional cases a length of 1½ m, but is 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.
The European Eel is a critically endangered species. Since the 1970s, the numbers of eels reaching Europe is thought to have declined by around 90% (possibly even 98%). Contributing factors include overfishing, parasites such as Anguillicola crassus, barriers to migration such as hydroelectric plants, and natural changes in the North Atlantic oscillation, Gulf Stream and the North Atlantic drift. Recent work suggests that PCB pollution may be a factor in the decline.
Eels have been important sources of food both as adults (including the famous jellied eels of East London) and as glass eels. Glass eel fishing using basket traps has been of significant economic value in many river estuaries on the western seaboard of Europe.
In captivity European eels can become very old.