Catadromy

Catadromy is a life-history pattern in which fish grow mainly in fresh water and migrate to the sea to reproduce. The European eel is its best-known example.

European eel: A catadromous eel native to European and North African waters that migrates to the Sargasso Sea to spawn. Its long migration is the best-known example of the catadromous life cycle.
Diadromy: A life-history pattern in which fishes migrate between fresh water and the sea for feeding or reproduction. Catadromy is one form of this broader two-way migration pattern.
American eel: A catadromous eel native to Atlantic and Gulf of Mexico waters that migrates to the Sargasso Sea to spawn. It is a second major example whose population status shapes North American management.
Eel reproduction: The reproductive biology of eels, including mating, spawning, and early development. Wild spawning has rarely been observed, leaving key details of catadromous reproduction unresolved.
Silver eel: The migratory adult stage of an eel, marked by physiological changes that prepare it for ocean travel. This is the eel's outward-migrating stage as it leaves freshwater for reproduction.
Anadromy: A life-history pattern in which fish grow mainly at sea and migrate to fresh water to reproduce. It reverses catadromy's usual direction between growth habitat and spawning habitat.
Eel ladder: A ramp or channel designed to help eels pass obstacles such as dams and weirs. These structures support upstream movement into freshwater growth habitats.
Eel migration: The movements of eels between continental waters and oceanic habitats during their life cycle. Routes, timing, and navigation cues remain difficult to establish across the ocean journey.
Sargasso Sea: A region of the North Atlantic bounded by ocean currents and characterized by floating Sargassum seaweed. European and American eels are thought to reproduce in this ocean region.
Amphidromy: A life-history pattern involving regular movement between fresh water and the sea, not primarily for reproduction. It also spans both habitats, but migration serves a different life-history purpose.

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