The European eel has a mysterious life cycle where it spends its early years in European rivers before migrating across the Atlantic Ocean to the Sargasso Sea near the Bahamas to spawn, although this has never been witnessed. The eggs hatch into larvae called leptocephalus that develop into glass eels and make the return journey to Europe, swimming into rivers. While in European rivers, the eels can grow up to 1 meter long before migrating back across the Atlantic to spawn, completing their long annual migration cycle.