he members of the family Salmonidae are commonly known as salmon. The other members of the family are trouts. Salmon roe is known as Salmo scientifically. Salmon dwell along the coasts of North Atlantic, Pacific Oceans and have been introduced into the Great Lakes of North America.
They are anadromous fishes which means that they are borne in freshwater and migrate to oceans and then return back to freshwater in order to reproduce. However, some species are restricted to fresh water only. They are produced in aquaculture on a mass scale in many parts of the globe.
Salmon prefer to lay eggs in a freshwater streams, particularly at high latitudes. The eggs hatch into sac fry or alevin. The sac fry, later on, transforms into parr which has well-demarcated camouflaging vertical stripes. The parr remains in the natal form for a period of six months to three years before becoming smolt.
Smolts have a characteristic bright silvery color with scales that are shed off easily. Only 10% of the salmon eggs are known to reach this stage. The body chemistry of the smolt is different from that of the parr and they are able to thrive in saltwater. Smolts spend most of their time migrating in the brackish waters.
Life cycle and growth
Salmon are known to spend 1-5 years of their life cycle in the open oceans where they become sexually mature. The adults then return back to the fresh waters for spawning. Before spawning, they undergo a number of changes. They develop hump and canine teeth which are known as kype particularly in males.
The silvery-blue color changes to darker shades. In all the species of Pacific salmon, the mature individuals die within few days or weeks of spawning. This trait is known as semelparity. Post spawning mortality in these fishes is very high.
In order to lay her roe female uses her caudal fin to make a depression known as redd by pulling out the gravel from the bottom of the water. The red may sometimes contain 5,000 eggs enclosing an area of 30 square feet. One or more males are known to approach the roe for spreading the milt over them.
The female then covers the eggs with gravel before moving to form another redd. Females may form as many as 7 redds before the supply of eggs is exhausted. Fish experiences rapid growth in summer while the growth rate reduces in winter.
Growth rings or annuli are formed which are analogous to that formed in tree trunks. Freshwater growth rings are formed in a more crowded form while the saltwater growth rings are spaced enough from each other.
Best medium for survival
Fresh water and estuaries form a perfect habitat for salmon. Older fishes also feed on other fishes. Developing embryos require cool water and good water flow for development. Mortality in the early stages is high because of predation by the predators as well as the change in aquatic habitat by human interference.
Salmon aquaculture is the major contributor to the world production of farmed fish providing a profit of about 1 billion to the United States ever year.
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Other cultured fishes include trout, tilapia, catfish and carp. Salmon farming is done on a mass scale in Chile, Norway, Scotland, Canada, America and Europe. They are carnivorous so they are fed on a meal prepared from the flesh of other fishes as well as other marine organisms.
Salmon farming requires more demand of wild fish in order to be used as food. The dietary requirement of salmon must be rich in proteins. Everyday about 2-4 kg of wild fish is caught in order to produce one kg of salmon.
High content of protein
Salmon are very frequently infected with myxozoan parasites. The parasites produce a milky fluid and remain embedded in the flesh of the fish. The life cycle of the parasite is complicated and the parasite is known to be transferred to the generations also.
Sea lice are also known to infect farm as well the wild salmon. Sea lice are ectoparasites feeding on blood, mucus and skin contents of the fish. Salmon is a food fish generally classified as oil fish because of high content of protein, high omega-3 fatty acids and vitamin D. It is also a source of cholesterol and the quantity of cholesterol ranges from 23-214 mg/100 gm depending on the species.
According to a report of the journal Science the flesh of farmed salmon has high levels of polychlorinated biphenyl about eight times high as compared to the wild salmon. Omega-3 content is also high in the farmed species. Omega-3 comes in three types ALA, DHA and EPA. Wild salmon are good source of DHA and EPA. Farmed salmon contains good percentage of ALA.
Colour and organ system
Salmon flesh is generally orange to red but the flesh of some wild species is white also. Salmon derives its natural color from the carotenoid pigments particularly astaxanthin and canthaxanthin. Wild salmon obtain these carotenoids by feeding on tin shellfishes and krills.
Astaxanthin is a potent antioxidant that stimulates the development of a healthy nervous system as well as enhances the fertility rate of the fish.
Research has shown that canthaxanthin has a negative effect on human eyes as they accumulate in the eyes. Canned salmon is a very popular delicacy in the United States and the Pacific Islands.
Smoked salmon is also a popular delicacy in many parts of the globe. Nowadays skinless and boneless canned salmon is also available in the markets. Salmon and salmon roe are used in making sushi and sashimi in Japan.
Salmon also holds an important position in mythology. They are important creatures of Celtic mythology and poetry. They are the symbols of wisdom and venerability. In Irish mythology, they are important animals of tales and poems. We can conclude that salmon is not only a food fish but also an important part of our literature and mythology.