ic salmon are considered much more aggressive than other salmon, and are more likely to attack other fish than others. Where they have become an invasive threat, attacking native salmon, such as Chinook salmon and coho salmon, has become a concern.
Breeding[edit source | edit]
Atlantic salmon breed in the rivers of Western Europe from northern Portugal north to Norway, Iceland, and Greenland, and the east coast of North America from Connecticut in the United States north to northern Labrador and Arctic Canada. Atlantic salmon which have escaped from the aquaculture industry have also been found breeding in rivers tributary to the Pacific Ocean in British Columbia on Canada's west coast. The species constructs a nest or "redd" in the gravel bed of a stream. The female creates a powerful downdraught of water with her tail near the gravel to excavate a depression. After she and a male fish have eggs and milt (sperm), respectively, upstream of the depression, the female again uses her tail, this time to shift gravel to cover the eggs and milt which have lodged in the depression.
Unlike the various Pacific salmon species which die after spawning (semelparous), the Atlantic salmon is iteroparous, which means the fish may recondition themselves and return to the sea to repeat the migration and spawning pattern several times, although most spawn only once or twice. Migration and spawning exact an enormous physiological toll on individuals, such that repeat spawners are the exception rather than the norm. Atlantic salmon show high diversity in age of maturity and may mature as parr, one- to five-sea-winter fish, and in rare instances, at older sea ages. This variety of ages can occur in the same population, constituting a ‘bet hedging’ strategy against variation in stream flows. So in a drought year, some fish of a given age will not return to spawn, allowing that generation other, wetter years in which to spawn.
Very young fertilised salmon eggs, notice the developing eyes and neural tube
A newly hatched Atlantic salmon alevin which, within around 24 hours, will absorb the yolk sac and become a fry
Hybridization[edit source | edit]
When in shared breeding habitats, Atlantic salmon will hybridize with brown trout (Salmo trutta). Hybrids between Atlantic salmon and brown trout were detected in two of four watersheds studied in northern [Spain]. The proportions of hybrids in samples of 'salmon' ranged from 0 to 7-7% but they were not significantly heterogeneous among locations, resulting in a mean hybridization rate of 2-3%. This is the highest rate of natural hybridization so far reported and is significantly greater than rates observed elsewhere in Europe.
Aquaculture[edit source | edit]
In its natal streams, Atlantic salmon are considered prized recreational fish, pursued by fly anglers during its annual runs. At one time, the species supported an important commercial fishery and a supplemental food fishery. However, the wild Atlantic salmon fishery is commercially dead; after extensive habitat damage and overfishing, wild fish make up only 0.5% of the Atlantic salmon available in world fish markets. The rest are farmed, predominantly from aquaculture in Norway, Chile, Canada, the UK, Ireland, Faroe Islands, Russia and Tasmania in Australia. Sport fishing communities, mainly from Iceland and Scandinavia, have joined in the North Atlantic Salmon Fund to buy away commercial quotas in an effort to save the wild species of Salmo salar.
Process[edit source | edit]
Adult male and female fish are anaesthetised; their eggs and sperm are "stripped" after the fish are cleaned and cloth dried. Sperm and eggs are mixed, washed, and placed into fresh water. Adults recover in flowing, clean, well-aerated water. Some researchers have even studied cryopreservation of their eggs.
Fry are generally reared in large freshwater tanks for 12 to 20 months. Once the fish have reached the smolt phase, they are taken out to sea, where they are held for up to two years. During this time, the fish grow and mature in large cages off the coasts of Canada, th