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Many types of fish undertake migrations on a regular basis, on time scales ranging from daily to annual, and with distances ranging from a few meters to thousands of kilometers. The purpose usually relates to either feeding or breeding; in some cases the reason for migration is still unknown.
Migratory fish are classified according to the following scheme:
1. 'diadromous' fish travel between salt and fresh water. ''(Greek: 'Dia' is between)'' There are three types of diadromous fish:

★ 'anadromous' fish live in the sea mostly, breed in fresh water ''(Greek: 'Ana' is up; The noun is "anadromy")''

★ 'catadromous' fish live in fresh water, breed in the sea ''(Greek: 'Cata' is down)''

★ 'amphidromous' fish move between fresh and salt water during some part of life cycle, but not for breeding ''(Greek: 'Amphi' is both)''
2. 'potamodromous' fish migrate within fresh water only. ''(Greek: 'Potamos' is river)''
3. 'oceanodromous' fish migrate within salt water only. ''(Greek: 'Oceanos' is ocean)''
The best-known anadromous fish are salmon, which hatch in small freshwater streams, go down to the sea and live there for several years, then return to the same streams where they were hatched, spawn, and die shortly thereafter. Salmon are capable of going hundreds of kilometers upriver, and humans must install fish ladders in dams to enable the salmon to get past. Other examples of anadromous fish are sea trout, three-spined stickleback, and shad.
The most remarkable catadromous fish are freshwater eels of genus ''Anguilla'', whose larvae drift on the open ocean, sometimes for months or years, before travelling thousands of kilometres back to their original streams (see ''eel reproduction'').
Diel vertical migration is a common behavior; many marine species move to the surface at night to feed, then return to the depths during daytime.
A number of large marine fishes, such as the tuna, migrate north and south annually, following temperature variations in the ocean. These are of great importance to fisheries.
Freshwater fish migrations are usually shorter, typically from lake to stream or vice versa, for spawning purposes.

Contents

See also

Reference

See also

★ DSSAM Model

★ Fish ladder

★ Hydrology transport model

★ Salinity

★ Stenohaline

★ Euryhaline

Reference

★ Carl E. Bond, ''Biology of Fishes'', 2nd ed. (Saunders, 1996), pp. 599-605.

★ Michael Blumm, J.D., Sacrificing the Salmon: A Legal and Policy History of the Decline of Columbia Basin Salmon, Bookworld Publications, 2002.