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Salmon is the common name for several species of fish of the family Salmonidae. Several other fish in the family are called trout. Salmon live in both the Atlantic and Pacific Oceans, as well as the Great Lakes and other land locked lakes. The Kamchatka Peninsula, in the Russian Far East, contains the world's greatest salmon sanctuary.


 


Typically, salmon are anadromous: they are born in fresh water, migrate to the ocean, then return to fresh water to reproduce. Folklore has it that the fish return to the exact spot where they were born to spawn and modern research shows that usually at least 90% of the fish spawning in a stream were born there. In Alaska, the crossing over to other streams allows salmon to populate new streams, such as those that emerge as a glacier retreats. The precise method salmon use to navigate has not been entirely established, though their keen sense of smell is certainly involved. In all species of Pacific salmon, the mature individuals die within a few days or weeks of spawning, a trait known as semelparity. Even in those species of salmon that may survive to spawn more than once (iteroparity), however, post-spawning mortality is quite high (perhaps as high as 40 to 50%.) Those species average about two or, perhaps, three spawning events per individual.

Coastal dwellers have long respected the salmon. Most peoples of the Northern Pacific shores had a ceremony to honor the first return of the year. For many centuries, people caught salmon as they swam upriver to spawn. A famous spearfishing site on the Columbia River at Celilo Falls was inundated after great dams were built on the river. The Ainu, of northern Japan, taught dogs how to catch salmon as they returned to their breeding grounds en masse. Now, salmon are caught in bays and near shore. Long drift net fisheries have been banned on the high seas except off the coast of Ireland.

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 supply oxygen) 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 conditions, 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.


When breeding, the female salmon excavates a shallow depression, called a redd, in the gravel of the streambed wherein she lays her eggs. The eggs usually range from orange to red in color. One or more males will approach the female as she deposits the eggs, fertilising them. The female then covers the eggs by disturbing the gravel at the upstream edge of the depression. The eggs will hatch into alevin or sac fry. The fry quickly develop into parr with camouflaging vertical stripes. The parr stay for one 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. The smolt body chemistry changes, allowing them to live in salt water. Smolts spend a portion of their out-migration time in brackish water, where their body chemistry becomes accustomed to osmoregulation in the ocean.

At sea, before their first return to freshwater, the juveniles are called grilse. They spend two to eight years (depending on the species) in the open ocean where they will become sexually mature. The adult salmon returns to its natal stream to spawn. When fish return for the first time they are called whitling in the UK. Prior to spawning, depending on the species, the salmon undergoes changes. They may grow a hump, develop canine teeth, develop a kype (a pronounced curvature of the jaws in male salmon). All will change from the silvery blue of a fresh run fish from the sea to a darker color. Condition tends to deteriorate the longer the fish remain in freshwater and they then deteriorate further after they spawn becoming known as kelts. Salmon can make amazing journeys, sometimes moving hundreds of miles upstream against strong currents and rapids, to reproduce.

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 Kingdom: Animalia

 Phylum: Chordata

 Class: Actinopterygii

 Superorder: Protacanthopterygii

 Order: Salmoniformes

 Family: Salmonidae