Migration
Migratory fish
250 species have an explicit migratory assignment. A salmon runs up a river to spawn; an eel runs down one and out to sea. The patterns below name the direction and the reason.
The total counts species with an explicit migratory assignment. Pattern counts also include suspected and conflicting assignments; a category can therefore exceed the total. Species may appear in several patterns, so these counts should not be added together.
- Potamodromous259 species
migrates within fresh water
- Diadromous52 species
moves between fresh water and the sea
- Anadromous52 species
spawns in fresh water, grows at sea
- Amphidromous34 species
moves between fresh water and the sea, but not to spawn
- SemiAnadromous32 species
spawns in fresh water, grows in an estuary
- Catadromous12 species
spawns at sea, grows in fresh water
Source
A database that disagrees with itself
The North American Freshwater Migratory Fish Database (USGS, 2021) files one row per published reference, so a species can carry several rows, and two references can assign it two different patterns.
The site does not pick a winner. A species whose references disagree shows every assignment on its own page, and says how many references were read.