Salmon, a book name for fishes of the genus Salmo, type of the Physostomous family Salmonidae, which also contains the trout, smelt, grayling, vendace, etc. The family has representatives in fresh and salt water, some migrating from one to the other; all food fishes, and most of them highly esteemed. The body is generally covered with scales, the head is naked, and there are no barbules. Behind the dorsal is an adipose fin ~ a mere fold of skin containing fat; the air-bladder is large and simple, and the spawn falls into the abdominal cavity before extrusion. In the type-genus the body is covered with small scales, the mouth-cleft is wide, and there are teeth on the jawbones, palatine bones, vomer and tongue. The anal fin is short. The young bear dark transverse bars, which disappear in the adults. This coloration has been compared to the spots of lion-cubs and some young deer. The geographical range of the genus is limited to the temperate and arctic zones of the northern hemisphere, their southernmost point in the Old World being the rivers of the Atlas and the Hindu Koosh, and in the New World the rivers falling into the head of the Gulf of California.
The Common Salmon (Salmo salar) is the largest and most valuable species of the genus, and the most shapely and beautiful of living fishes. On the upper surface the colour is bluish- or greenish-grey, fading into silvery-white below, and above the lateral line, which is nearly straight, there is a plentiful sprinkling of large black spots. The hinder edge of the gill-cover is rounded. Fish brought to market usually range from 20 lbs. to 40 lbs. in weight. Buckland noted one from the Tay that scaled 73 lbs., and specimens of from 83 lbs. to 93 lbs. are on record. Fish of such a size, however, are very rare, and will grow rarer, owing to the systematic way in which rivers are fished for the market. The adult male is easily distinguished from the female by the protrusion of the lower jaw, and in the breeding season this is developed into a kind of hook, which becomes a formidable weapon in combats with rivals, and with it mortal mjuries are sometimes inflicted. During the summer salmon are found along the coast and in estuaries, entering rivers about the autumn, though the time varies in different rivers, the temperature of the water being probably an important factor in the matter. As a general rule, salmon return to spawn in the rivers in which they were bred. The work of ascending to the upper reaches is often one of great difficulty. The fish move chiefly by night, and are able to pass over a perpendicular obstacle of about six feet in height. To afford them assistance in their journey, fish-ladders are fixed, which serve as landings or resting-places whence fresh leaps can be taken. On arriving at the spawning ground the female sweeps away the gravel with her tail, and in the trench so formed deposits her ova, the male keeping guard the while. When she has finished her task he swims over the place shedding the milt which fertilises them. As soon as this is done a few sweeps of her tail cover the ova with gravel, and the spawning, which generally occupies about ten days, is completed, and the spent fish are ready to return to the sea. A period of from 90 to 120 days is required to hatch the eggs, but this term varies according to the temperature of the water, and is consequently longer in the Scotch than in the English, salmon streams. The eggs, too, have many enemies, and but a very small proportion of the fry that come out ever reaches the sea. When born the young fish still bear the umbilical vesicle attached, and it is not absorbed for some weeks. The form of the fry is probably as well known as that of the full-grown fish, for the former are well-known microscopic "objects" readily obtainable from any dealer in such wares, and they will live and thrive in an aquarium where there is plenty of vegetation and an abundance of "water-fieas." Few descend to the sea in the first year. It was formerly thought that the migration was always delayed till the second year; but there is evidence that in fish artificially bred the migration of at least a part of them takes place earlier. On the return to fresh water the fish are generally sexually mature, and on their subsequent descent to the sea they assume the character of adults. In its different stages of growth the salmon has a variety of names. According to Dr. Day, the fish in its full-grown condition is known as the salmon; one on its second return from the sea is often termed a gerling in the Severn, or a botcher on its first return, when under five pounds weight, although the more general designation is grilse; when under two pounds weight it is usually termed salmon peal by fishmongers. From one to two years before it has gone to the sea it is known as a parr, pink, smolt, smelt, salmon-fry, sprag, or salmon-spring (Northumberland), samlet, brandling, fingerling, b1ack-fin, blue-fin, shed, skegger, gravelling, hepper, laspring, gravel laspring, skerling, or sparling in Wales. In Northumberland a milter or spawning male is known as a summercock or gib-fish, and a salmon as a simen. In the Severn a salmon which has remained in fresh-water during the summer without going to the sea is a laurel. After spawning this fish is a kelt or slat, but a male is generally termed a kipper and a female a shedder or baggit.
The Pacific Salmon belong to the closely-allied genus Onchorhynchus, differing only from the type-genus in the increased nnmber of rays in the anal fin. There are five species, from the rivers of the North Pacific, the most important, the Quinnat or King Salmon (0. quinnat); the annual take of this fish in the Columbia river averages 30,000,000 lbs., of which a large proportion is canned for European markets; the Blue-back Salmon (0. nerka). The former reaches a weight of 100 lbs; that of the latter ranges from 4 lbs. to 8 lbs. The flesh of salmon is of a pinkish-orange colour, probably due to the crustaceans which form their principal food.