The genus Oncorhynchus (family Salmonidae) contains the many subspecies of Pacific salmon (seven species) and Pacific trout (four species). Oncorhynchus is placed in the family Salmonidae, along with two other genera: Salmo (mostly trouts of European origin) and Salvelinus (char). Relationships among salmonid species have long been controversial, and the many studies of molecular and fossil data have shown inconsistencies.

The name Oncorhynchus is derived from the Greek onkos ("hook") and rynchos ("nose"), in reference to the hooked jaws (the "kype") that males develop in the mating season. Most Oncorhynchus species are anadromous (migrate between salt and fresh water), some strains migrate enormous distances (traveling up to 2500 miles from home) between Pacific waters and the Bering sea and crossing international boundaries which complicate management issues for these desirable fish. After feeding at sea the fish leave the ocean, often to overcome huge obstacles on their way to return to the same part of their natal stream. They do not feed when they return to streams and all anadromous strains except the Steelhead are semelparous (die after spawning).

The complicated life histories and limited ranges of Oncorhynchus strains make them particularly vulnerable to extinction due to human activities. Wilson and Turner (2009) write, “All species and subspecies in this group are threatened, endangered, sensitive, or species of conservation concern in portions of their native ranges”. Habitat destruction, hydroelectric dams, and overfishing have contributed to the serious decline and extinction of Oncorhynchus species. For many native strains, competition from hatchery fish, including the Atlantic salmon (Salmo salar) recently introduced into Pacific waters, is also a factor of great concern for survival.

(Angler innovations; NOAA ESA status listings; Pacific Salmon Commission; U.S. Fish and Wildlife Service; Wikipedia 2012; Wilson and Turner 2009)