anadromous

 Describing a fish that is born in freshwater, migrates to the ocean to grow and mature, and returns to freshwater to spawn. Salmon are the archetype — hatching in gravel streams, spending years in the open Pacific, then navigating thousands of miles back to the exact stream of their birth to reproduce and, in the case of Pacific salmon, to die. The word names a life organized around a single, epic, one-way return.