Oncorhynchus is a genus of fish in the family Salmonidae; it contains the Pacific salmon and Pacific trout. The name of the genus is derived from the Greek ὄγκος (ónkos, lump, bend) + ῥύγχος (rhúnkhos, snout), in reference to the hooked snout (the kype) that the males develop during mating season. Salmon and trout with native ranges in waters draining to the Pacific Ocean are members of the genus. Their range extends from Beringia southwards, roughly to Taiwan in the west and Mexico to the east. In North America, some subspecies of O. clarkii are native in the Rocky Mountains and Great Basin, while others are native to the Rio Grande and western tributaries of the Mississippi River Basin which drain to the Gulf of Mexico (Atlantic ocean), rather than to the Pacific. Several species of Oncorhynchus have been introduced into non-native waters around the globe, establishing self-sustaining wild populations. The six Pacific salmons of Oncorhynchus are anadromous (migratory) and semelparous (die after spawning). Migration can be affected by parasites. Infected individuals can become weak and probably have shortened lifespans. Infection with parasites creates an effect known as culling whereby fish that are infected are less likely to complete the migration. Anadromous forms of Oncorhynchus mykiss known as steelhead are iteroparous. The coastal cutthroat trout (Oncorhynchus clarkii clarkii) is considered semi-anadromous, as it spends some time in the ocean, usually much closer to its native stream than its fully anadromous relatives. Currently, 12 species and numerous subspecies in this genus are recognized
