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Wednesday, March 4, 2009

is the common name for several species of fish of the family Salmonidae. Several other fish in the family are called trout, the difference is often attributed to the migratory life of the salmon as compared to the residential behaviour of trout, this holds true for the Salmo genus. Salmon live in both the Atlantic (one migratory species Salmo salar) and Pacific Oceans, as well as the Great Lakes (approximately a dozen species of the genus Oncorhynchus).

Typically, salmon are anadromous: they are born in fresh water, migrate to the ocean, then return to fresh water to reproduce. However, there are rare species that can only survive in fresh water habitats. This is most likely due to the domestication of these certain species of Salmon. Folklore has it that the fish return to the exact spot where they were born to spawn, tracking studies have shown this to be true but the nature of how this memory works has long been debated.

Salmon is a popular food. Consuming salmon is considered to be healthy due to the fish's high protein, high Omega-3 fatty acids, and high vitamin D[8] content. Salmon is also a source of cholesterol, ranging 23–214 mg/100g depending on the species.[9] 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 specimens, 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 (alpha-linolenic 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 Atlantic salmon outnumber wild Atlantic salmon 85 to 1.[10]Aquaculture

Artificially-incubated chum salmonSalmon 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 and the island of 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. 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 2-4 kg of wild caught fish to produce one kg of salmon.[23]

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 and non profit groups like the Cook Inlet Aquaculture Association 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 concrete 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 prophylactic chemicals to control diseases.

Farm raised salmon are fed the carotenoids astaxanthin and canthaxanthin, so that their flesh color matches wild salmon.