Salmon Swimming Upstream In Ketchikan Creek 3

Salmon () is the common name for several commercially important species of euryhaline ray-finned fish from the family Salmonidae, which are native to tributaries of the North Atlantic (genus ''Salmo'') and North Pacific (genus ''Oncorhynchus'') basin. Other closely related fish in the same family include trout, char, grayling, whitefish, lenok and taimen.

Salmon are typically anadromous: they hatch in the gravel beds of shallow fresh water streams, migrate to the ocean as adults and live like sea fish, then return to fresh water to reproduce. However, populations of several species are restricted to fresh water throughout their lives. Folklore has it that the fish return to the exact spot where they hatched to spawn, and 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.

Salmon are important food fish and are intensively farmed in many parts of the world, with Norway being the world's largest producer of farmed salmon, followed by Chile. They are also highly prized game fish for recreational fishing, by both freshwater and saltwater anglers. Many species of salmon have since been introduced and naturalized into non-native environments such as the Great Lakes of North America, Patagonia in South America and South Island of New Zealand.

Species

The term "salmon" comes from the Latin ''salmo'', which in turn might have originated from ''salire'', meaning "to leap". The seven commercially important species of salmon occur in two genera. The genus ''Salmo'' contains the Atlantic salmon, found in both sides of the North Atlantic, as well as more than 40 other species commonly named as trout. The genus ''Oncorhynchus'' contains 12 recognised species which occur naturally only in the North Pacific, six of which are known as Pacific salmon while the remainder are considered trout. Outside their native habitats, Chinook salmon have been successfully introduced in New Zealand and Patagonia, while coho, freshwater sockeye and Atlantic salmon have been established in Patagonia, as well.

    ^† Both the ''Salmo'' and ''Oncorhynchus'' genera also contain a number of species referred to as trout. Within ''Salmo'', additional minor taxa have been called salmon in English, i.e. the Adriatic salmon (''Salmo obtusirostris'') and Black Sea salmon (''Salmo labrax''). The steelhead anadromous form of the rainbow trout migrates to sea, but it is not termed "salmon".

Also, there are several other species which are not true salmon, as in the above list but have common names which refer to them as being salmon. Of those listed below, the Danube salmon or ''huchen'' is a large freshwater salmonid related to the salmon above, but others are marine fishes of the unrelated Perciformes order:

''Eosalmo driftwoodensis'', the oldest known Salmoninae fish in the fossil record, helps scientists figure how the different species of salmon diverged from a common ancestor. The British Columbian salmon fossil provides evidence that the divergence between Pacific and Atlantic salmon had not yet occurred 40 million years ago. Both the fossil record and analysis of mitochondrial DNA suggest the divergence occurred 10 to 20 million years ago. This independent evidence from DNA analysis and the fossil record indicate that salmon divergence occurred long before the glaciers (of Quaternary glaciation) began their cycle of advance and retreat.

Distribution

*Atlantic salmon (''Salmo salar'') reproduce in northern rivers on both coasts of the Atlantic Ocean.
**Landlocked salmon (''Salmo salar'' m. ''sebago'') live in a number of lakes in eastern North America and in Northern Europe, for instance in lakes Sebago, Onega, Ladoga, Saimaa, Vänern, and Winnipesaukee. They are not a different species from the Atlantic salmon but have independently evolved a non-migratory life cycle, which they maintain even when they could access the ocean.
*Chinook salmon (''Oncorhynchus tshawytscha'') are also known in the United States as king salmon or blackmouth salmon, and as spring salmon in British Columbia. Chinooks are the largest of all Pacific salmon, frequently exceeding . The name tyee is used in British Columbia to refer to Chinook over 30 pounds, and in the Columbia River watershed, especially large Chinooks were once referred to as June hogs. Chinook salmon are known to range as far north as the Mackenzie River and Kugluktuk in the central Canadian arctic, and as far south as the Central California coast.
*Chum salmon (''Oncorhynchus keta'') is known as dog, keta, or calico salmon in some parts of the US. This species has the widest geographic range of the Pacific species: in the eastern Pacific from north of the Mackenzie River in Canada to south of the Sacramento River in California and in the western Pacific from Lena River in Siberia to the island of Kyūshū in the Sea of Japan.
*Coho salmon (''Oncorhynchus kisutch'') are also known in the US as silver salmon. This species is found throughout the coastal waters of Alaska and British Columbia and as far south as Central California (Monterey Bay). It is also now known to occur, albeit infrequently, in the Mackenzie River.
*Masu salmon or cherry salmon (''Oncorhynchus masou'') are found only in the western Pacific Ocean in Japan, Korea, and Russia. A landlocked subspecies known as the Taiwanese salmon or Formosan salmon (''Oncorhynchus masou formosanus'') is found in central Taiwan's Chi Chia Wan Stream.
*Pink salmon (''Oncorhynchus gorbuscha''), known as humpies in southeast and southwest Alaska, are found in the western Pacific from Lena River in Siberia to Korea, found throughout northern Pacific, and in the eastern Pacific from the Mackenzie River in Canada to northern California, usually in shorter coastal streams. It is the smallest of the Pacific species, with an average weight of .
*Sockeye salmon (''Oncorhynchus nerka'') is also known in the US (especially Alaska) as red salmon. This lake-rearing species is found in the eastern Pacific from Bathurst Inlet in the Canadian Arctic to Klamath River in California, and in the western Pacific from the Anadyr River in Siberia to northern Hokkaidō island in Japan. Although most adult Pacific salmon feed on small fish, shrimp, and squid, sockeye feed on plankton they filter through gill rakers. Kokanee salmon are the landlocked form of sockeye salmon.
*Danube salmon, or huchen (''Hucho hucho''), are the largest permanent freshwater salmonid species.

Life cycle

Salmon eggs are laid in freshwater streams typically at high latitudes. The eggs hatch into alevin or sac fry. The fry quickly develop into parr with camouflaging vertical stripes. The parr stay for six months to three years in their natal stream before becoming smolts, which are distinguished by their bright, silvery colour with scales that are easily rubbed off. Only 10% of all salmon eggs are estimated to survive to this stage.

The smolt body chemistry changes, allowing them to live in salt water. While a few species of salmon remain in fresh water throughout their life cycle, the majority are anadromous and migrate to the ocean for maturation: in these species, smolts spend a portion of their out-migration time in brackish water, where their body chemistry becomes accustomed to osmoregulation in the ocean. This body chemistry change is hormone-driven, causing physiological adjustments in the function of osmoregulatory organs such as the gills, which leads to large increases in their ability to secrete salt. Hormones involved in increasing salinity tolerance include insulin-like growth factor I, cortisol, and thyroid hormones, which permits the fish to endure the transition from a freshwater environment to the ocean.

The salmon spend about one to five years (depending on the species) in the open ocean, where they gradually become sexually mature. The adult salmon then return primarily to their natal streams to spawn. Atlantic salmon spend between one and four years at sea. When a fish returns after just one year's sea feeding, it is called a grilse in Canada, Britain, and Ireland. Grilse may be present at spawning, and go unnoticed by large males, releasing their own sperm on the eggs.

Prior to spawning, depending on the species