Diadromous fish are fish that migrate between freshwater and saltwater. The migration patterns differ for each species and have seasonal and lifecycle variations. Diadromous fish are unique--only one percent of all fish in the world are diadromous.
Some diadromous fish migrate great distances, while others migrate much shorter distances. In either case, these fish undergo physiological changes that allow them to survive as they migrate from freshwater to saltwater or vice versa. There are several types of diadromous fish, differing in their specific migration patterns:
Anadromous fish spend most of their adult lives in salt water, and migrate to freshwater rivers and lakes to reproduce. East Coast anadromous fish species include alewife, striped bass, Atlantic salmon, and shortnose sturgeon. West Coast anadromous species include five salmon species, steelhead, white sturgeon, and American shad (non-native).
Catadromous fish spend most of their adult lives in freshwater, and migrate to saltwater to spawn. Juvenile fish migrate back upstream where they stay until maturing into adults, at which time the cycle starts again. The only catadromous species in the United States is the American eel. American eels migrate thousands of miles to spawn in the Sargasso Sea, located in the mid-Atlantic ocean, south of Bermuda and north of the Bahamas.
