Diadromous
The general word for fish that move between fresh and salt water during their lives.
Also: amphidromous
Diadromous fish regularly migrate between the sea and fresh water. The word covers anadromous fish, which breed in rivers, catadromous fish, which breed at sea, and amphidromous fish, which move between the two for feeding rather than breeding, as many gobies of tropical islands do. Only about one per cent of fish species are diadromous, but they include some of the most valuable, such as salmon, hilsa and eels, and their journeys link rivers to the sea.