§ Species Oncorhynchus is a genus of ray-finned fish in the subfamily Salmoninae of the family Salmonidae, native to coldwater tributaries of the North Pacific basin.

The name of the genus is derived from the Ancient Greek ὄγκος (ónkos, 'lump, bend') + ῥύγχος (rhúnkhos, 'snout'), in reference to the hooked secondary sexual characteristic — known as the kype — that the males develop on the lower jaw tip during mating season.

Salmon and trout within Onchorhynchus are native to the tributaries of the North Pacific Ocean, with their native ranges extend from the Bering Sea coasts southwards to as far as Taiwan in the west and Mexico in the east, although most of them are distributed in high-latitude cold waters from the Russian Far East to the Pacific Northwest.

In North America, some subspecies of cutthroat trout (O. clarkii) have become landlocked populations native to endorheic waters in the Rocky Mountains and the Great Basin, while others have crossed the Continental Divide to inhabit the Rio Grande and western tributaries of the Mississippi River, both of which drain into the Gulf of Mexico instead of the Pacific Ocean.

Several species of Oncorhynchus, such as the rainbow trout (O. mykiss) and Chinook salmon (O. tshawytscha), have been widely introduced into non-native waters around the globe, establishing self-sustaining wild populations.

Several Late Miocene (about 7 million years ago (Mya)) trout-like fossils in Idaho, in the Clarkia Lake beds, appear to be of Oncorhynchus.

[3] Montgomery (2000) discusses the pattern of the fossil record as compared to tectonic shifts in the plates of the Pacific Northwest of America.

The climatic and habitat changes that would follow such a geologic event are discussed, in the context of potential stressors leading to adaptation and speciation.

As the result of western expansion and development in the U.S., experts estimate salmon populations in the Columbia River basin had been reduced to less than 20% of their pre-1850 levels by 1933.

[9] Declines are attributed to a wide variety of causes—overfishing, habitat loss and degradation, artificial propagation, stocking, and hybridization with or competition with introduced, non-native species.

[10] Salmon body size is decreasing due to a variety of evolutionary forces, including dams,[12] fishing practices,[10] climate change,[13] and increased competition in the ocean.

[19] Pacific salmon are harvested throughout the world as a source of food in countries ranging from the United States to South Korea.

In Japanese chum salmon, for example, between 1970 and 1988 there has been a continuous decrease in body weight averaging between 11 and 32 percent.

[21] In part, this decline in body weight has been related to the size selective effect of fishing gear used in the harvesting of salmon populations.

However, studies have also shown that for Pacific salmon, a larger mean size at the time of reproduction increases the survival of offspring.

Canada has also used the Species at Risk Act to recognize the importance of biological diversity when it comes to the conservation of the salmon population.

In British Columbia sockeye salmon in four different watersheds were certified by the Marine Stewardship Council, or MSC, as sustainable fisheries in July 2010 and the certification is good for a period of five years.

The Alaska Department of Fish and Game first received MSC, Marine Stewardship Council, Certification in sustainable seafood back in 2000.

[26] Other efforts of the Wild Salmon Center include combating illegal fishing, maintaining sustainable fisheries, and creating local watersheds as new habitats.

Chinook from Chile were released into Argentinean rivers and there were stockings of Coho and Sockeye Salmon and Rainbow Trout in Patagonia.

[35] Thus, in 1989, taxonomic authorities moved the Rainbow, Cutthroat and other Pacific basin trouts into the genus Oncorhynchus.