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For other uses, see Salmon (disambiguation).
Spawning sockeye salmon in Becharof Creek, Becharof Wilderness, Alaska
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.
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. 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 involved. In all species of Pacific salmon, the mature individuals die within a few days or weeks of spawning, a trait known as semelparity. However, even in those species of salmon that may survive to spawn more than once (iteroparity), post-spawning mortality is quite high (perhaps as high as 40 to 50%.)
Salmon has long been at the heart of the culture and livelihood of coastal dwellers. Most peoples of the Northern Pacific shore 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.
Salmon population levels are of concern in the Atlantic and in some parts of the Pacific but in Alaska stocks are still abundant. Fish farming is outlawed and the State of Alaska\'s fisheries management system is viewed as the global leader in the management of wild, sustainable fish stocks. The most important Alaska Salmon wild sustainable fisheries are located near the Kenai River, Copper River, and in Bristol Bay. In Canada, the Skeena River wild salmon returning which support commercial fisheries, aboriginal food fisheries, sports fisheries and the area\'s diverse wildlife on the coast and around communities hundreds of miles inland in the watershed. The Columbia River salmon population is now less than 3% of what it was when Lewis and Clark arrived at the river.Endangered Salmon. U.S. Congressman Jim McDermott. Retrieved on 2006-11-17.
Both Atlantic and Pacific Salmon are important to recreational fishing around the world.
Contents |
Illustration of a male Coho Salmon
Eggs in different stages of development. In some only a few cells grow on top of the yolk, in the lower right the blood vessels surround the yolk and in the upper left the black eyes are visible, even the little lens
Salmon fry hatching - the larva has grown around the remains of the yolk - visible are the arteries spinning around the yolk and little oildrops, also the gut, the spine, the main caudal blood vessel, the bladder and the arcs of the gills
In order to lay her roe, the female salmon uses her tail fin to excavate a shallow depression, called a redd. The redd may sometimes contain 5,000 eggs covering 30 square feet.McGrath, Susan. Spawning Hope. Audubon Society. Retrieved on 2006-11-17. The eggs usually range from orange to red in color. One or more males will approach the female in her redd, depositing his sperm, or milt, over the roe.Pacific Salmon, (Oncorhynchus spp.). U.S. Fish and Wildlife Services. Retrieved on 2006-11-17. 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 will make as many as 7 redds before her supply of eggs is exhausted. The salmon then die within a few days of spawning.
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. It is estimated that only 10% of all salmon eggs survive long enough to reach this stage.A Salmon\'s Life: An Incredible Journey. U.S. Bureau of Land Management. Retrieved on 2006-11-17. 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.
The salmon spend one to five years (depending on the species) in the open ocean where they will become sexually mature. The adult salmon returns primarily to its natal stream to spawn. When fish return for the first time they are called whitling in the UK and grilse or peel in Ireland. 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. Chinook and sockeye salmon from central Idaho, for example, travel over 900 miles and climb nearly 7000 feet from the Pacific ocean as they return to spawn.
Each year, the fish experiences a period of rapid growth, often in summer, and one of slower growth, normally in winter. This results in rings (annuli) 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 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.
Edouard Manet: Still Life with Salmon
Filet of an Atlantic SalmonSalmon is a popular food. Consuming salmon is considered to be reasonably healthy due to the fish\'s high protein, high Omega-3 fatty acids, and high vitamin DDietary Supplement Fact Sheet: Vitamin D. National Institutes of Health. Archived from the original on 2007-12-13. Retrieved on 2007-12-13. content. Salmon is also a source of cholesterol, ranging 23–214 mg/100g depending on the species.Cholesterol: Cholesterol Content in Seafoods (Tuna, Salmon, Shrimp). Retrieved on 2007-12-13. According to reports in the journal Science, however, farmed salmon may contain high levels of dioxins. PCB (polychlorinated biphenyl) levels may be up to eight times higher in farmed salmon than in wild salmon. Omega-3 content may also be lower than in wild caught individuals, and in a different proportion to what is found naturally. Omega 3 comes in three types, ALA, DHA and EPA; wild salmon has traditionally been an important source of DHA and EPA, which are important for brain function and structure, among other things. This means that if the farmed salmon is fed on a meal which is partially grain then the amount of Omega 3 it contains will be present as ALA (Linoleic acid). The body can itself convert ALA Omega 3 into DHA and EPA, but at a very inefficient rate (2–15%). Nonetheless, according to a 2006 study published in the Journal of the American Medical Association, the benefits of eating even farmed salmon still outweigh any risks imposed by contaminants [1]. Type of Omega 3 present may not be a factor for other important health functions. A simple rule of thumb is that the vast majority of Atlantic salmon available on the world market are farmed (greater than 99%), whereas the majority of Pacific salmon are wild-caught (greater than 80%). Farmed salmon outnumber wild salmon 85 to 1.Montaigne. Everybody Loves Atlantic Salmon: Here\'s the Catch.... National Geographic. Retrieved on 2006-11-17.
Raw salmon in Japanese styleSalmon flesh is generally orange to red in colour, although there are some examples of white fleshed wild salmon. The natural colour of salmon results from carotenoid pigments, largely astaxanthin (E161j), in the flesh.Opinion of the Scientific Committee on Animal Nutrition on the use of canthaxanthin in feedingstuffs for salmon and trout, laying hens, and other poultry. (PDF) 6–7. European Commission - Health & Consumer Protection Directorate. Retrieved on 2006-11-13. Wild salmon get these carotenoids from eating krill and other tiny shellfish. Because consumers have shown a reluctance to purchase white fleshed salmon, astaxanthin, and very minutely canthaxanthin (E161g)), are added as artificial colourants to the feed of farmed salmon because prepared diets do not naturally contain these pigments. In most cases the astaxanthin is made chemically; alternatively it is extracted from shrimp flour. Another possibility is the use of dried red yeast, which provides the same pigment. However, synthetic mixtures are the least expensive option. Astaxanthin is a potent antioxidant that stimulates the development of healthy fish nervous systems and that enhances the fish\'s fertility and growth rate. Research has revealed canthaxanthin may have negative effects on the human eye, accumulating in the retina at high levels of consumption. Today the concentration of carotenoids (mainly canthaxanthin and astaxanthin) exceeds 8 mg/kg of flesh and all fish producers try to reach a level that represents a value of 16 on the "Roche Color Card", a colour card used to show how pink the fish will appear at specific doses. This scale is specific for measuring the pink colour due to astaxanthin and is not for the orange hue obtained with canthaxanthin. The development of processing and storage operations, which can be detrimental on canthaxanthin flesh concentration, has led to an increased quantity of pigments added to the diet to compensate for the degrading effects of the processing. In wild fish, carotenoid levels of up to 20–25 mg are present, but levels of canthaxanthin are, in contrast, minor.
Canned salmon in the U.S. is usually wild Pacific catch, though some farmed salmon is available in canned form. Smoked salmon is another popular preparation method, and can either be hot or cold smoked. Lox can refer either to cold smoked salmon or to salmon cured in a brine solution (also called gravlax).
Raw salmon flesh may contain Anisakis nematodes, marine parasites that cause Anisakiasis. Before the availability of refrigeration, the Japanese did not consume raw salmon. Salmon and salmon roe have only recently come into use in making sashimi (raw fish) and sushi.
Poached salmon |
White Alaskan Salmon.jpg
White Alaskan Salmon |
Salmon roe.jpg
Salmon roe at the Shiogama seafood market in Japan |
Salmon- Egg Membranes.jpg
Ovary of the salmon was opened and loosened |
Salade de jambon cru et saumon fume.jpg
Salad with ham and smoked salmon |
Salmon die shortly after spawning. This one was photographed at a spawning site along Eagle Creek in Oregon.
Many wild Salmon stocks have seen a marked decline in recent decades, especially north Atlantic populations which spawn in western European and eastern Canadian waters, and wild salmon of the Snake and Columbia River systems in the Northwest USA. The causes of these declines likely include a number of factors, among them:
There are efforts to relieve this situation. As such, several governments and NGOs are sharing in research and habitat restoration efforts.
Beavers\' ponds may provide critical habitat for juvenile salmon. An example of this was seen in the years following 1818 in the Columbia River Basin. In 1818, the British government made an agreement with the U.S. government to allow U.S. citizens access to the Columbia catchment (see Treaty of 1818). At the time, the Hudson\'s Bay Company sent word to trappers to extirpate all furbearers from the area in an effort to make the area less attractive. In response to the elimination of beavers from large parts of the river system, salmon runs plummeted, even in the absence of many of the factors usually associated with the demise of salmon runs. Salmon recruitment can be effected by beavers\' dams because dams can:Northwest Power and Conservation Council. Extinction. Retrieved on 2007-12-21.K. D. Hyatt, D. J. McQueen, K. S. Shortreed and D. P. Rankin. Sockeye salmon (Oncorhynchus nerka) nursery lake fertilization: Review and summary of results. Retrieved on 2007-12-21.M. M. Pollock, G. R. Pess and T. J. Beechie. The Importance of Beaver Ponds to Coho Salmon Production in the Stillaguamish River Basin, Washington, USA. Retrieved on 2007-12-21.
Beavers\' dams are able to nurture salmon juveniles in Estuarine tidal marshes where the salinity is less than 10ppm. Beavers build small dams of generally less than 2 feet high in channels in the Myrtle zone. These dams can be overtopped at high tide and hold water at low tide. This provides refuges for juvenile salmon so they don\'t have to swim into large channels where they are subject to predation.An overlooked ecological web.
Artificially-incubated chum salmon
Salmon aquaculture is the major economic contributor to the world production of farmed fin-fish, representing over $1 billion US annually. Other commonly cultured fish species include: tilapia, catfish, sea bass, carp, bream, and trout. Salmon farming is very big in Chile, Norway, Scotland, Canada and the Faroe Islands, and is the source for most salmon consumed in America and Europe. Atlantic salmon are also, in very small volumes, farmed in Russia, Tasmania, Australia.
Salmon are carnivorous and are currently fed a meal produced from catching other wild fish and other marine organisms. Consequently, as the number of farmed salmon increase, so does the demand for other fish to feed the salmon. Work continues on substituting vegetable proteins for animal proteins in the salmon diet. Unfortunately though, this substitution results in lower levels of the highly valued Omega-3 content in the farmed product. But still the farmed salmon contains more Omega-3 than what is found in wild salmon. Intensive salmon farming now uses open net cages which have low production costs but have the drawback of allowing disease and sea lice to spread to local wild salmon stocks.
On a dry-dry basis, it takes 10 kg of wild caught fish to produce one kg of salmon. The other 9kg enters the sea in the form of faeces and to some extent, uneaten food. In areas with low currents, this organic material collects on the bottom and turns anaerobic. Salmon farms (feed lots actually as there is no farming involved) introduce levels of untreated sewage into the ocean that has already been outlawed for sea side communities.
Another form of salmon production, which is safer but less controllable, is to raise salmon in hatcheries until they are old enough to become independent. They are then released into rivers, often in an attempt to increase the salmon population. This practice was very common in countries like Sweden before the Norwegians developed salmon farming, but is seldom done by private companies, as anyone may catch the salmon when they return to spawn, limiting a company\'s chances of benefiting financially from their investment. Because of this, the method has mainly been used by various public authorities as a way of artificially increasing salmon populations in situations where they have declined due to overharvest, construction of dams, and habitat destruction or disruption. Unfortunately, there can be negative consequences to this sort of population manipulation, including genetic "dilution" of the wild stocks, and many jurisdictions are now beginning to discourage supplemental fish planting in favour of harvest controls and habitat improvement and protection. A variant method of fish stocking, called ocean ranching, is under development in Alaska. There, the young salmon are released into the ocean far from any wild salmon streams. When it is time for them to spawn, they return to where they were released where fishermen can then catch them.
An alternative method to hatcheries is to use spawning channels. These are artificial streams, usually parallel to an existing stream with cement or rip-rap sides and gravel bottoms. Water from the adjacent stream is piped into the top of the channel, sometimes via a header pond to settle out sediment. Spawning success is often much better in channels than in adjacent streams due to the control of floods which in some years can wash out the natural redds. Because of the lack of floods, spawning channels must sometimes be cleaned out to remove accumulated sediment. The same floods which destroy natural redds also clean them out. Spawning channels preserve the natural selection of natural streams as there is no temptation, as in hatcheries, to use propholactic chemicals to control diseases.
Farm raised salmon are fed the dye astaxanthin (3,3\'-hydroxy-β,β-carotene-4,4\'-dione), a carotenoid pigment, so that their flesh color matches wild salmon.Pigments in Salmon Aquaculture: How to Grow a Salmon-colored Salmon. Retrieved on 2007-08-26. “Astaxanthin (3,3\'-hydroxy-β,β-carotene-4,4\'-dione) is a carotenoid pigment, one of a large group of organic molecules related to vitamins and widely found in plants. In addition to providing red, orange, and yellow colors to various plant parts and playing a role in photosynthesis, carotenoids are powerful antioxidants, and some (notably various forms of carotene) are essential precursors to vitamin A synthesis in animals.”
According to Canadian biologist Dr. Dorothy Kieser, protozoan parasite Henneguya salminicola is commonly found in the flesh of salmonids. It has been recorded in the field samples of salmon returning to Queen Charlotte Island streams. The fish responds by walling off the parasitic infection into a number of cysts that contain milky fluid. This fluid is an accumulation of a large number of parasites.
Henneguya and other parasites in the myxosporean group have a complex lifecycle where the salmon is one of two hosts. The fish releases the spores after spawning. In the Henneguya case, the spores enter a second host, most likely an invertebrate, in the spawning stream. When juvenile salmon out-migrate to the Pacific Ocean, the second host releases a stage infective to salmon. The parasite is then carried in the salmon until the next spawning cycle. The myxosporean parasite that causes whirling disease in trout has a similar lifecycle.Crosier, Danielle M.. Whirling Disease – Myxobolus cerebralis. Retrieved on 2007-12-13. However, as opposed to whirling disease, the Henneguya infestation does not appear to cause disease in the host salmon - even heavily infected fish tend to return to spawn successfully.
According to Dr. Kieser, a lot of work on Henneguya salminicola was done by scientists at the Pacific Biological Station in Nanaimo in the mid-1980, in particular, an overview report N.P. Boyce, Z. Kabata and L. Margolis (1985). "Investigation of the Distribution, Detection, and Biology of Henneguya salminicola (Protozoa, Myxozoa), a Parasite of the Flesh of Pacific Salmon". Canadian Technical Report of Fisheries and Aquatic Sciences (1450): 55. which states that "the fish that have the longest fresh water residence time as juveniles have the most noticeable infections. Hence in order of prevalence coho are most infected followed by sockeye, chinook, chum and pink." As well, the report says that, at the time the studies were conducted, stocks from the middle and upper reaches of large river systems in British Columbia such as Fraser, Skeena, Nass and from mainland coastal streams in the southern half of B.C. "are more likely to have a low prevalence of infection." The report also states "It should be stressed that Henneguya, economically deleterious though it is, is harmless from the view of public health. It is strictly a fish parasite that cannot live in or affect warm blooded animals, including man".
According to Klaus Schallie, Molluscan Shellfish Program Specialist with the Canadian Food Inspection Agency, "Henneguya salminicola is found in southern B.C. also and in all species of salmon. I have previously examined smoked chum salmon sides that were riddled with cysts and some sockeye runs in Barkley Sound (southern B.C., west coast of Vancouver Island) are noted for their high incidence of infestation."
As noted above, the Lepeophtheirus salmonis, a sea louse, causes deadly infestations of farm-grown and wild salmon. On the Pacific coast of Canada, the louse-induced mortality of pink salmon is commonly over 80%. Climate change in Washington is a possible cause of disease.
The various species of salmon have many names, and varying behaviors.
Atlantic salmon
Atlantic ocean species belong to the genus Salmo. They include,
Pacific species belong to the genus Oncorhynchus, some examples include;
In Irish mythology, the hero Fionn mac Cumhaill, leader of the Fianna, gained powers of perception from a salmon. The young Fionn met the poet Finegas near the river Boyne and studied under him. Finegas had spent seven years trying to catch the salmon of knowledge which lived in a pool on the Boyne, for whoever ate the salmon would gain all the knowledge in the world. Eventually he caught it and told the boy to cook it for him. While cooking it Fionn burst a blister on the salmon\'s skin, burning his thumb, and instinctively put his thumb in his mouth, swallowing a piece of the salmon\'s skin. This imbued him with the salmon\'s wisdom.Fenian Cycle attributed to Oisín
In Norse mythology, when Loki, god of mischief and strife, tricked Hod the blind god into killing Baldr, god of beauty and light, Loki jumped into a river and transformed himself into a salmon in order to escape punishment from the other gods. When they held out a net to trap him he attempted to leap over it but was caught by Thor who grabbed him by the tail with his hand, and this is why the salmon\'s tail is tapered.Prose Edda by Snorri Sturluson
Durham Ranger, a classic design of salmon fly used in the sport of fly fishing.
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