rout from its use in the Idylls of the poet Ausonius (4th century CE).
Physiology[edit source | edit]
This is a fairly large salmonid, with average adult specimens measuring 71 to 76 cm (28 to 30 in) long and weighing 3.6 to 5.4 kg (7.9 to 12 lb). Record-sized specimens have been measured to a maximum of 153 cm (60 in) and a weight of 45 kg (99 lb). The colouration of young Atlantic salmon does not resemble their adult stage. While they live in fresh water, they have blue and red spots. While they mature, they take on a silver-blue sheen. When adult, the easiest way of identifying them is by the black spots predominantly above the lateral line, although the caudal fin is usually unspotted. When they reproduce, males take on a slight green or red colouration. The salmon has a fusiform body, and well-developed teeth. All fins, save the adipose, are bordered with black.
Distribution and habitat[edit source | edit]
At sea, the species is found mainly in the waters off Greenland and in migrations to and from its natal streams, along the northern eastern and western Atlantic coasts. Wild salmon disappeared from many rivers during the twentieth century due to overfishing and habitat change. By 2000 the numbers of Atlantic salmon had dropped to critically low levels.
Diet[edit source | edit]
Young salmon begin a feeding response within a few days. After the yolk sac is absorbed by the body, they begin to hunt. Juveniles start with tiny invertebrates, but as they mature, they may occasionally eat small fish. During this time, they hunt both in the substrate and in the current. Some have been known to eat salmon eggs. The most commonly eaten foods include caddisflies, blackflies, mayflies, and stoneflies.
Behaviour[edit source | edit]
Fry and parr have been said to be territorial, but evidence showing them to guard territories is inconclusive. While they may occasionally be aggressive towards each other, the social hierarchy is still unclear. Many have been found to school, especially when leaving the estuary.
Adult Atlantic 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 