catadromie

Catadromy is a migratory pattern in which mature individuals live and feed in freshwater and migrate to the ocean to spawn. It is the opposite of anadromy, where fish mature in the sea and migrate into freshwater to reproduce. The best-known catadromous group is the eels of the family Anguillidae, including the European eel (Anguilla anguilla) and the American eel (Anguilla rostrata).

In their life cycle, eggs hatch in the marine environment into leptocephalus larvae, which drift with ocean currents toward continental areas. These larvae metamorphose into glass eels, become elvers as they enter freshwater systems, and then grow into yellow eels. When mature, many catadromous species migrate back to the sea to spawn, and in some species these adults die after reproduction. The spawning phase for eels involves long-distance migrations to suitable marine environments, followed by larval stages that return to coastal and estuarine zones.

The spawning grounds for Atlantic eel species are widely believed to lie in the Sargasso Sea, where adults migrate to reproduce. After spawning, the offspring disperse, and the cycle continues as young eels enter freshwater habitats. Catadromy is a specialized strategy that links freshwater and marine ecosystems, often involving complex physiological changes to cope with osmoregulation across different salinities.

Conservation concerns for catadromous fishes, especially eels, include barriers to migration such as dams, habitat loss, pollution, and overfishing. Protected status and international management efforts aim to preserve migratory routes and breeding populations.

Etymology derives from Greek, with katá meaning down or back and dromos meaning running or course, reflecting the backward migration from sea to inland water bodies for reproduction.