SALMON AND SALMONIDAE. The salmonoids are soft-rayed fishes with abdominal pelvic fins, generally with an adipose fin, a pneumatic duct to the air-bladder with oviducts absent or incomplete, and with ribs attached to small separate bones wedged into pits in the centra of the vertebrae. The group includes three northern families, the Salmonidae, the Osmeridae (see SMELT) and the Salangidae, little white fishes of the seas of China and Japan. Three families, Argentinidae, Microstomidae and Ophisthoproctidae, are strictly marine, mostly oceanic. Three others, Retropinnatidae, Haplochitonidae and Galaxiidae, are southern, found on the coasts and in the rivers of Patagonia, Australia and New Zealand.
The Salmonidae are the most generalized family, distinguished by having the last two or three vertebrae turned upwards. They inhabit arctic and northern seas, and the fresh waters of Europe, northern Asia and North Amer ica; the marine species enter rivers to breed. There are eight genera, which may be distinguished as follows : I. Parietals not meeting. Scales small, 19 or more from origin of dorsal fin to lateral line. Dorsal fin short, of io to 16 rays. A double or zig-zag series of teeth along vomer in middle of roof of mouth Salmo A group of teeth on head of vomer Salvelinus A curved series of teeth across head of vomer, connecting the palatine series ; mouth large Hucho A straight series of teeth across head of vomer, connecting the palatine series : mouth smaller Brachymystax II. Parietals meeting. Scales larger, 13 or less from origin of dorsal to lateral line.
A. Dorsal fin short, of io to 16 rays.
Teeth small, in bands Stenodus Teeth vestigial or absent Coregonus B. Dorsal fin longer, of 18 to 24 rays.
Mouth rather large; teeth strong Phylogephyra Mouth smaller; teeth moderate Thymallus Some of these genera are described in other articles, namely Salvelinus (CHAR), Coregonus (WHITEFisH) and Thymallus (GRAYLING). Hucho includes the huchen of the Danube, a large predacious fish with somewhat pike-like head, and two other species, respectively from Siberia, and from northern Saghalien and Yesso. Brachymystax has a single species from Siberia, and Stenodus one only, a large migratory fish, entering the Mackenzie river and arctic rivers of Siberia.
The genus Salmo is by far the most important, and includes the black-spotted fish generally known as salmon and trout.
The Salmon (S. salar) is fusi form, with conical head; it is silvery, with scattered blackish spots; the mouth is moderately large with conical teeth in the jaws, and on the palate and tongue. It inhabits the north At lantic, ranging from Hudson bay, Iceland and northern Europe to Cape Cod and the Bay of Biscay. It feeds on herring, mackerel, sand-eels, etc., and enters rivers throughout the year, breeding on gravelly shallows from Septem ber to February. The fresh-run fish are silvery, with red flesh full of fat; they do not feed in the rivers and the sexual glands are developed at the expense of the other tissues, so that the flesh becomes pale and watery; in the breeding fish the silvery coloration is replaced by a dull grey or brown, and in the males especially large black spots edged with white and irregular red spots appear on the body; the skin is thick and spongy, with the scales imbedded in it ; in the males the front teeth are enlarged, the jaws are prolonged, and the lower is hooked upwards. These peculiarities of the breeding fish are probably due to their ab normal physiological condition while fasting and transferring sub stance from the muscles to the genital glands. The female fish scoops out a trough in the gravel, and sinking into it deposits some eggs which are fertilized by the male; she then covers the eggs with gravel by strokes of the tail, burying them at a depth of about a foot. The eggs are about in. in diameter; they hatch out at the end of the winter. The fry, or alevins, have a large yolk-sac, which provides their nourishment for a month or two, during which they live in the gravel; then the young fish, a little more than an inch long, emerge and swim in shoals, feeding on crustaceans, insects, etc. Generally in about two years, but less in southern waters and more in the north, they attain a length of about six inches, and then migrate to the sea.