Salmon: Facts about Fish

This edited article about salmon originally appeared in Look and Learn issue number 930 published on 17 November 1979.

Few fish have occupied the attention of mankind as much as the salmon – that extraordinary fish that divides its time between the sea and fresh water rivers to which it returns to spawn.

Salmon. The salmon may leap twenty falls like this to reach the breeding ground for egg laying

It was known as the food of kings among the ancient Irish, and it was forbidden to those who were not of royal birth. In Welsh mythology, it was a symbol of wisdom, and for some of the North American Indian tribes it typified physical prowess. Legends about it abound.

Many of them are of an ecclesiastical nature, such as the legend of St. Kentigern, the first bishop of Glasgow, who was said to have recovered a certain virtuous lady’s lost ring from the belly of a salmon. This event is commemorated in the arms of the city, which include the salmon with the ring in its mouth.

Until recent times, little was known about the salmon, beyond the fact that it hatches out in rivers and makes its way to the sea, and that it later returns to the river and spawns there – a behaviour pattern which, it is thought, goes back far into its evolutionary history.

In Britain, the annual salmon “run” into fresh water takes place from September until the end of January. The salmon that have reached maturity in the sea enter the estuaries of their favourite rivers and make their way far upstream to the shallow waters near the source.

Their journey has always been the cause of wonderment to those who have studied them. Rushing waterfalls drive them back, but only temporarily; rock pools are cleared with a single leap; and raging currents are breasted with seeming ease.

As if this were not enough, they have to contend also with a legion of enemies in the shape of predatory trout and pike which devour them wholesale.

But the glittering hordes sweep on, driven by an age-old instinct, until the survivors finally reach the spawning ground. Here the female scoops out a deep trough, known as the redd, and deposits her eggs. The male follows close behind and fertilises them.

The redd and its contents are then covered with gravel. This spawning period may extend over a period of more than two weeks, and often several nests are used by the same pair of fish.

The eggs hatch in a month to five months, depending on the warmth of the waters in which they hatch out. When they do, the larval salmon leaves the egg. This is provided with a yolk, which the young eats before wriggling through the gravel to find food.

This is known as the “alevin” stage and at its termination the fish, now nearly a year old, are recognisable as little salmon, known as “parr”. They remain in fresh water for up to two years, when a silvery sheen develops on the body.

The fish are now called “smolts”, and it is at this stage of their development that they begin to congregate in large companies, in preparation for their journey down to the sea.

In the rich feeding grounds of the ocean, they grow sleek and plump, with the firm flesh which we usually associate with the salmon. During this period of their existence, they are known as “grilse”. A few years later, they set off for their spawning grounds.

Because they do not eat during this epic journey upstream, the salmon are exhausted and many of them are unable to return to the sea alive. Those that do manage to survive are then known as “kelts”.

Naturalists have now discovered that the life history of a particular adult salmon can usually be established by studying its scales. As the fish grows more rapidly in the sea, the scale rings are spaced farther apart than they would be during its freshwater period. The fish also carries spawning scars, which tells us how many times the fish has bred.

There are two main strains of salmon, the Atlantic, which is found on the western coasts of Europe and along the eastern coasts of North America, and the Pacific, of which there are six species. These are a less hardy breed that, having once spawned, never reaches the sea again.

Emaciated and weak from its efforts to reach the spawning ground, the Pacific salmon invariably falls prey to parasites and disease long before it reaches the sea.

Although both species have been subjected to a great deal of study, we still have a lot to learn about this magnificent fish.

Salmon are among the many creatures about whose survival conservationists are concerned. The pollution of seas and rivers presents a continuing threat. Another danger comes from excessive trapping. For commercial purposes the fish are netted in large numbers as they swim up-river for spawning.

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