Salmon is the common name for several species of fish in the family Salmonidae. Other fish in the same family include trout, char, grayling and whitefish. Salmon are native to tributaries of the North Atlantic (genus Salmo) and Pacific Ocean (genus Oncorhynchus). Many species of salmon have been introduced into non-native environments such as the Great Lakes of North America and Patagonia in South America. Salmon are intensively produced in aquaculture in many parts of the world.
Typically, salmon are anadromous: they are born in fresh water, migrate to the ocean, then return to fresh water to reproduce. However, populations of several species are restricted to fresh water through their lives. Various species of salmon display anadromous life strategies while others display freshwater resident life strategies. Folklore has it that the fish return to the exact spot where they were born to spawn; tracking studies have shown this to be mostly true. A portion of a returning salmon run may stray and spawn in different freshwater systems. The percent of straying depends on the species of salmon. Homing behavior has been shown to depend on olfactory memory.
The term "salmon" comes from the Latin salmo, which in turn may have originated from salire, meaning "to leap". The nine commercially important species of salmon occur in two genera. The genus Salmo contains the Atlantic salmon, found in the north Atlantic, as well as many species commonly named trout. The genus Oncorhynchus contains eight species which occur naturally only in the north Pacific. As a group, these are known as Pacific salmon. Chinook salmon have been introduced in New Zealand and Patagonia. Coho, Kokanee and Atlantic salmon have been established in Patagonia as well. There are also a number of other species whose common names refer to them as being salmon. Of those, the Danube salmon or huchen is a large freshwater salmonid related to the salmon.
Freshwater streams and estuaries provide important habitat for many salmon species. They feed on terrestrial and aquatic insects, amphipods, and other crustaceans while young, and primarily on other fish when older. Eggs are laid in deeper water with larger gravel, and need cool water and good water flow (to supply oxygen) to the developing embryos. Mortality of salmon in the early life stages is usually high due to natural predation and human-induced changes in habitat, such as siltation, high water temperatures, low oxygen concentration, loss of stream cover, and reductions in river flow. Estuaries and their associated wetlands provide vital nursery areas for the salmon prior to their departure to the open ocean. Wetlands not only help buffer the estuary from silt and pollutants, but also provide important feeding and hiding areas.
Salmon not killed by other means show greatly accelerated deterioration (phenoptosis, or "programmed aging") at the end of their lives. Their bodies rapidly deteriorate right after they spawn as a result of the release of massive amounts of corticosteroids.
For now, the only two members of the family which can be caught are: