Salmon (fish)

I

Introduction

Salmon (fish), common name applied to fish characterized by an elongate body covered with small, rounded scales and a fleshy fin between the dorsal fin and tail. These fish belong to the salmon family, which also includes char (see Trout), grayling, and whitefish. Most members of the salmon family are valuable food fish and excellent game fish. Salmon eat smaller fishes, crustaceans, and insects. They are found in both fresh and salt water in the colder regions of the northern hemisphere.

II

Salmon Life Cycle

Many species of salmon are anadromous—they spawn, or lay their eggs, in fresh water; the young migrate to salt water and grow up there; and the fish return to fresh water to breed after they reach maturity. Other populations or species of salmon are landlocked, spending their entire life cycle in fresh water. The migratory instinct of members of the salmon family is remarkably specific, each generation returning to spawn in exactly the same breeding places as the generation before it. Some salmon migrate hundreds or even thousands of miles to reach their spawning grounds. Even those species that do not migrate from fresh water to salt water spawn in the same freshwater streams as did their ancestors.

Although usually drab in color before the breeding season, which varies with the species, members of the salmon family develop bright hues at spawning time. During this season the male usually develops a hooked snout and a humped back. Salmon typically spawn in rapidly flowing, clear streams with gravel and rocks in the bottom. Before mating, one parent excavates a nest, or redd, for the eggs. The female deposits eggs in the nest and the male releases sperm, or milt, over the eggs to fertilize them. The female then stirs up the stream bottom so that earth and stones cover the eggs and protect them. During the migrations and nest-building activity that precede mating, neither the females nor the males consume food.

The eggs hatch in two weeks to six months, depending on the species and the water temperature. The newly hatched young, called alevins, remain buried in the nest, living on nutrients absorbed from a yolk sac attached to the abdomen. When all the yolk has been absorbed, the young salmon, then called fry or fingerlings, emerge from the gravel to seek food. Their diet consists of microscopic plants and small animals, such as insects.

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As the fry feed and grow larger, dark vertical bars appear along their sides. At this stage they are referred to as parr or brandlings. The amount of time the young salmon spend in fresh water depends on the species. Eventually the young salmon turn bright silver and, in the case of seagoing forms, descend to the sea. At this stage they are called smolts. When they are fully grown and reach sexual maturity, the salmon begin the migration back to fresh water to reproduce. Different species of salmon spend different amounts of time in salt water before migrating back to their birth stream to spawn.

III

Atlantic Salmon

The Atlantic salmon has tasty flesh that is often orange-red. The fish average about 3.6 to 5.5 kg (8 to 12 lb) in weight, but specimens weighing up to 38 kg (84 lb) have been caught. The Atlantic salmon migrates from the sea into cold fresh water in late spring or early summer, swimming upriver at an average rate of up to 6.4 km (4 mi) per day. The female lays as many as 20,000 eggs in October or November, after which time the adult salmon float downstream and return to the sea. An Atlantic salmon returning to its spawning ground for the first time is known as a grilse. After spawning, it is known as a kelt. The Atlantic salmon returns year after year to its breeding place and can live for up to 8 years.

Several subspecies of the Atlantic salmon live in the lakes of the northern United States without ever descending to sea. These landlocked salmon are much smaller than migrating salmon, attaining a maximum weight of about 16 kg (about 35 lb). The two most important landlocked populations of the Atlantic salmon are the Sebago salmon, found in lakes from New Hampshire to New Brunswick, and the ouananiche, of Lac Saint-Jean, Canada.

IV

Pacific Salmon

Salmon found in the North Pacific Ocean spawn only once, dying after depositing and fertilizing their eggs. Six species of salmon live in the Pacific Ocean: chinook, sockeye, coho, pink, chum, and masu. The best-known and most valuable species is the chinook salmon, which is also known as the king salmon, Columbia River salmon, quinnat, chowichee, and takou. The chinook is the largest species of Pacific salmon, averaging about 7 to 11 kg (15 to 25 lb) in weight. Numerous specimens up to 1.5 m (5 ft) in length and 60 kg (130 lb) in weight have been recorded. The chinook salmon migrates farther than any other salmon, often traveling 1,600 to 3,200 km (1,000 to 2,000 mi) inland to its spawning ground.

The sockeye, also known as red or blue-black salmon, is another valuable species. Young sockeye salmon live for a year or two in a lake before migrating to the sea. A small, landlocked subspecies of sockeye is known as the kokanee. Another valuable fishery is based on the coho, or silver salmon, which has tasty, light pink flesh. Other salmon in the eastern Pacific are the pink, or humpback salmon, and the chum, or dog salmon. The masu salmon, the smallest species of Pacific salmon, lives only in the waters of Japan.

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