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I N D E X
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Many species of Salmon are anadromous and migrate long distances up rivers and streams to spawn.

Many types of fish migrate on a regular basis, on time scales ranging from daily to annual, and over distances ranging from a few meters to thousands of kilometers. Fish usually migrate because of diet or reproductive needs, although in some cases the reason for migration remains unknown.

Contents

Classification

  • potamodromous fish migrate within fresh water only (Greek: Potamos is river).
  • oceanodromous fish migrate within salt water only (Greek: 'Oceanos' is ocean).
  • diadromous fish travel between salt and fresh water (Greek: 'Dia' is between).
  • anadromous fish live in the ocean mostly, and breed in fresh water (Greek: 'Ana' is up; The noun is "anadromy")
  • catadromous fish live in fresh water, and breed in the ocean (Greek: 'Cata' is down)
  • amphidromous fish move between fresh and salt water during their life cycle, but not to breed (Greek: 'Amphi' is both)

Examples

Some of the best-known anadromous fish are the five species of Pacific salmon, which are Chinook (King), Coho (Silver), Sockeye (Red), Chum (Dog) and Pink (Humpback). The salmon hatch in small freshwater streams. From there they migrate to the sea to mature, living there for two to six years. When mature, the salmon return to the same streams where they were hatched to spawn. 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 fishes are sea trout, three-spined stickleback, and shad.

Life cycle of anadromous fish. From a U.S. Federal Government pamphlet. (Click image to enlarge.)

The most remarkable catadromous fishes 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 life history).

An example of an make an amphidromous species is the Bull shark, which lives in Lake Nicaragua of Central America and the Zambezi River of Africa. Both these habitats are fresh water, yet Bull sharks will also migrate to and from the ocean. Specifically, Lake Nicaragua Bull sharks migrate to the Atlantic Ocean and Zambezi Bull sharks migrate to the Indian Ocean.

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.

Historic exploitation

Since prehistoric times humans have exploited certain anadromous fishes during their migrations into freshwater streams, when they are more vulnerable to capture. Societies dating to the Millingstone Horizon are known which exploited the anadromous fishery of Morro Creek1 and other Pacific coast estuaries. In Nevada the Paiute tribe has harvested migrating Lahontan cutthroat trout along the Truckee River since prehistoric times. This fishing practice continues to current times, and the U.S. EPA has supported research to assure the water quality in the Truckee can support suitable populations of the Lahontan cutthroat trout.

See also

Notes

  1. ^ C.M. Hogan, 2008

References
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