An amphihaline species is a migratory species of which the life cycle alternates between the marine environment and a fresh water environment.
This is the case of the Atlantic salmon (Salmo salar), the sturgeon (Acipenser sturio) or the European eel (Anguilla anguilla).
Eel larvae, called leptocephalus, are born in the Sargasso Sea. Three years later, carried by the Gulf Stream, they reach the European coast (mainly France and Spain). At the end of their journey, they become young fish, called elver or baby eels, which thrive in fresh water. They swim up watercourses and undergo a new process of metamorphosis, after which they turn into eels and are able to live in very little water. As they approach sexual maturity, eels return to the sea, swim into the depths and return to the Sargasso Sea, to fertilise and lay their eggs. The entire cycle takes several years to complete and is still mysterious. © Arnaud Richard / Onema