Anadromous
Living mostly in the sea but swimming up rivers to spawn, as salmon, hilsa, shad and many sturgeons do.
Also: anadromy
Anadromous fish grow up at sea, where food is plentiful, and return to fresh water to breed. Pacific salmon swim up the rivers where they hatched, often finding them by smell, spawn once and die. The hilsa moves from the Bay of Bengal into the Padma, Meghna and Hooghly during the monsoon, and its arrival sets the fishing season in Bangladesh and West Bengal. Shad, many sturgeons and the sea lamprey do the same. Dams and barrages that block the way upriver are a leading cause of decline for these fish.