What term describes fish migrations that take place entirely within fresh water?

The term for fish migrations that take place entirely within fresh water is potamodromous. It describes movement between freshwater habitats, such as a lake and an inlet stream, without entering the sea.

The word contrasts with anadromous migration, in which fish live mainly in the ocean but move into fresh water to spawn, as salmon do. Catadromous fish, such as freshwater eels, make the reverse breeding journey from rivers to the sea. Oceanodromous fish migrate wholly within marine waters.

Potamodromous migration is often connected with spawning, feeding, or seasonal changes in water conditions. Trout commonly move upstream from lakes or larger rivers to shallow gravel beds, while some river fish travel long distances to reach traditional spawning grounds. Dams and other barriers can disrupt these routes.

The classification was formalized in the mid-20th century. Ichthyologist George S. Myers introduced potamodromous alongside broader terms such as diadromous and amphidromous in a 1949 treatment of fish migration. The key point is the habitat boundary: potamodromous movement never crosses from fresh water into the ocean.