Which eel species migrates from Japanese rivers to the Mariana Trench to spawn?

The Japanese eel migrates from East Asian rivers to the western North Pacific near the West Mariana Ridge to spawn.

Japanese eels (Anguilla japonica) are catadromous: they grow in freshwater and coastal habitats, then swim thousands of kilometers offshore to reproduce. Their spawning area lies west of the Mariana Islands, near underwater seamounts associated with the West Mariana Ridge—not at the deepest floor of the Mariana Trench.

The eels spawn around the new moon, and their eggs and newly hatched larvae drift westward in the North Equatorial Current. The larvae develop into transparent, leaf-shaped leptocephali before becoming glass eels and eventually reaching Asian rivers.

A common mix-up is confusing this species with American and European eels, which spawn in the Sargasso Sea. Japanese eels are also not permanently freshwater fish; their life cycle connects rivers, estuaries, and the open ocean.