Salmon
Salmon are any of several commercially important species of euryhaline ray-finned fish from the genera Salmo and Oncorhynchus of the family Salmonidae, native to tributaries of the North Atlantic and North Pacific basins. Salmon is a colloquial or common name used for fish in this group, but is not a scientific name. Other closely related fish in the same family include trout, char, grayling, whitefish, lenok and taimen, all coldwater fish of the subarctic and cooler temperate regions with some sporadic endorheic populations in Central Asia.
Salmon are typically anadromous: they hatch in the shallow gravel beds of freshwater headstreams and spend their juvenile years in rivers, lakes and freshwater wetlands, migrate to the ocean as adults and live like sea fish, then return to their freshwater birthplace to reproduce. However, populations of several species are restricted to fresh waters throughout their lives. Folklore has it that the fish return to the exact stream where they themselves 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.
Name and etymology
The Modern English term salmon is derived from, samon and saumon, which in turn are from Anglo-Norman: saumon, from, and from . The unpronounced "l" absent from Middle English was later added as a Latinisation to make the word closer to its Latin root. The term salmon has mostly displaced its now dialectal synonym lax, in turn from, from, from from Proto-Indo-European: *lakso-.Species
The seven commercially important species of salmon occur in two genera of the subfamily Salmoninae. 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, sockeye and Atlantic salmon have been established in Patagonia, as well.† Both the Salmo and Oncorhynchus genera also contain a number of trout species informally referred to as salmon. Within Salmo, the Adriatic salmon and Black Sea salmon have both been named as salmon in English, although they fall outside the generally recognized seven salmon species. The masu salmon is actually considered a trout in Japan, with masu actually being the Japanese word for trout. On the other hand, the steelhead and sea trout, the anadromous forms of rainbow trout and brown trout respectively, are from the same genera as salmon and live identical migratory lives, but neither is termed "salmon".
The extinct 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 Eocene salmon's fossil from British Columbia 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 during the Miocene. This independent evidence from DNA analysis and the fossil record indicate that salmon divergence occurred long before the Quaternary glaciation began the cycle of glacial advance and retreat.
Non-salmon species of "salmon"
There are several other species of fish which are colloquially called "salmon" but are not true salmon. Of those listed below, the Danube salmon or huchen is a large freshwater salmonid closely related to the seven species of salmon above, but others are fishes of unrelated orders, given the common name "salmon" simply due to similar shapes, behaviors and niches occupied:Distribution
- Atlantic salmon reproduce in northern rivers on both coasts of the Atlantic Ocean.
- *Landlocked Atlantic salmon is a potamodromous subspecies/morph that 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 sea-run Atlantic salmon but have independently evolved a freshwater-only life cycle, which they maintain even when they could access the ocean.
- Chinook salmon are also known in the United States as king salmon or "blackmouth salmon", and as "spring salmon" in British Columbia, Canada. Chinook salmon is the largest of all Pacific salmon, frequently exceeding and. The name tyee is also used in British Columbia to refer to Chinook salmon 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 Californian Coast.
- Chum salmon is known as dog salmon or calico salmon in some parts of the US, and as keta in the Russian Far East. 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 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. It is also now known to occur, albeit infrequently, in the Mackenzie River.
- Masu salmon, also known as "cherry trout" in Japan, are found only in the western Pacific Ocean in Japan, Korea, and Russian Far East. A landlocked subspecies known as the Taiwanese salmon or Formosan salmon is found in central Taiwan's Chi Chia Wan Stream.
- Pink salmon, known as humpback salmon or "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 is also known as red salmon in the US. 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 Hokkaido 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 a landlocked form of sockeye salmon. Their appeal to sport fishermen has led to them being introduced to many places in the United States and Canada.
- Danube salmon, or huchen, are the largest permanent freshwater salmonid species.
Life cycle
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 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, salmon undergo changes. They may grow a hump, develop canine-like teeth, or develop a kype. All change from the silvery blue of a fresh-run fish from the sea to a darker colour. Salmon can make amazing journeys, sometimes moving hundreds of miles upstream against strong currents and rapids to reproduce. Chinook and sockeye salmon from central Idaho, for example, travel over and climb nearly from the Pacific Ocean as they return to spawn. Condition tends to deteriorate the longer the fish remain in fresh water, and they then deteriorate further after they spawn, when they are known as kelts. In all species of Pacific salmon, the mature individuals die within a few days or weeks of spawning, a trait known as semelparity. Between 2 and 4% of Atlantic salmon kelts survive to spawn again, all females. However, even in those species of salmon that may survive to spawn more than once, postspawning mortality is quite high.
To lay her roe, the female salmon uses her tail, to create a low-pressure zone, lifting gravel to be swept downstream, excavating a shallow depression, called a redd. The redd may sometimes contain 5,000 eggs covering. The eggs usually range from orange to red. One or more males approach the female in her redd, depositing sperm, or milt, over the roe. The female then covers the eggs by disturbing the gravel at the upstream edge of the depression before moving on to make another redd. The female may make as many as seven redds before her supply of eggs is exhausted.
Each year, the fish experiences a period of rapid growth, often in summer, and one of slower growth, normally in winter. This results in ring formation around an earbone called the otolith, analogous to the growth rings visible in a tree trunk. Freshwater growth shows as densely crowded rings, sea growth as widely spaced rings; spawning is marked by significant erosion as body mass is converted into eggs and milt.
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 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 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.