and forming the lateral margin of the upper jaw. Pseudobranchiæ present. Gillrakers varying with the species. Opercula complete. No barbels. Dorsal fin of moderate length, placed near the middle of the length of the body. Adipose fin well developed. Caudal fin forked. Anal fin moderate or rather long. Ventral fins nearly median in position. Pectoral fins inserted low. Lateral line present. Outline of belly rounded. Vertebræ in large number, usually about 60. Skeleton not strongly ossified. The stomach in all the Salmonidæ is siphonal, and at the pylorus are many (15 to 200) comparatively large pyloric cæca. The air-bladder is large. The eggs are usually much larger than in fishes generally, and the ovaries are without special duct, the ova falling into the cavity of the abdomen before exclusion. The large size of the eggs, their lack of adhesiveness, and the readiness with which they may be impregnated, render the Salmonidæ peculiarly adapted for artificial culture.
The Salmonidæ belong to the order of Isospondyli, the most primitive and least specialized of the orders of Teleostei or bony fishes. In their group, these fishes represent a high degree of development, adaptation to swift rivers and the need of complex instincts. The Salmonidæ are peculiar to the North Temperate and Arctic regions, and within this range they are almost equally abundant wherever suitable waters occur. Some of the species, especially the larger ones, are marine and anadromous, living and growing in the sea, and ascending fresh waters to spawn. Still others live in running brooks, entering lakes or the sea when occasion serves, but not habitually doing so. Still others are lake fishes, approaching the shore or entering brooks in the spawning season, at other times retiring to waters of considerable depth. Some of them are active, voracious, and gamy; while others are comparatively defenseless, and will not take the hook. They are divisible into 10 easily recognized genera—Coregonus, Argyrosomus, Plecoglossus, Brachymystax, Stenodus, Hucho, Oncorhynchus, Salmo, Cristivomer, and Salvelinus.
The Atlantic salmon (Salmo salar) is the most familiar, although commercially not the most important of the various species properly called salmon. It is the only black-spotted salmonoid found on the Atlantic seaboard of America. (For illustration, see Colored Plate of American Food Fishes, accompanying article Fish as Food.) In Europe, where black-spotted trout (Salmo fario) and salmon trout (Salmo trutta) also occur, the true salmon may be distinguished by the fact that the teeth on the shaft of the vomer mostly disappear with age. From the only other species (Salmo trutta) positively known which shares this character, the salmon may be known by the presence of but 11 scales between the adipose fin and the lateral line.
The salmon of the Atlantic is, as already stated, an anadromous fish, spending most of its life in the sea, and entering the streams in the fall for the purpose of reproduction. The time of running varies much in different streams and also in different countries. As with the Pacific species, these salmon are not easily discouraged in their progress, leaping cascades 10 or 12 feet in height, and other obstructions; or, if these prove impassable, dying after repeated fruitless attempts. The young salmon, or ‘parr,’ is hatched in the spring. It usually remains about two years in the rivers, descending at about the third spring to the sea, when it is known as ‘smolt.’ The dusky cross-shades found in the young salmon or parr are characteristic of the young of nearly all the Salmonidæ. In the sea it grows much more rapidly, and becomes more silvery in color, and is known as ‘grilse.’ The grilse rapidly develop into the adult salmon; and some of them, as is the case with the grilse of the Pacific salmon, are capable of reproduction. After spawning, the salmon are very lean and unwholesome, in appearance, as in fact, and are then known as ‘kelts.’ The Atlantic salmon does not ascend rivers to any such distances as those traversed by the quinnat and the blue-back; its kelts for the most part survive the act of spawning. As a food-fish, the Atlantic salmon is similar to the quinnat salmon, although rather less oily. The average weight of the adult is probably less than 15 pounds. The largest one recorded was taken on the coast of Ireland in 1881, and weighed 84¾ pounds.
The salmon is found in Europe between the latitudes of 45° and 75°. In the United States it is now rarely seen south of Cape Cod, although formerly the Hudson and numerous other rivers were salmon streams. The land-locked forms of salmon, abundant in Norway, Sweden, Maine, and Quebec, which cannot, or at least do not, descend to the sea, should probably not be considered as distinct species. Comparison has been made of numerous specimens of the common land-locked salmon (Salmo salar, var. sebago) from the lakes of Maine and New Brunswick with land-locked salmon (Salmo salar, var. hardini) from the lakes of Sweden, and with numerous migratory salmon, both from America and Europe. While showing minor distinctions, especially in size and habit, they are structurally identical. The differences are not greater than would be expected on the hypothesis of recent adaptation of the salmon to lake life. We have, therefore, on our Atlantic coast but one species of salmon (Salmo salar).
The numerous other species of the genus Salmo are usually known as ‘trout,’ although, except for the better development of the vomer and greater backward extension of the series of teeth upon it, there is no technical character of any importance to distinguish the Atlantic salmon from the true, or black-spotted trout. But the salmon reaches a larger size than any of these, and it is regularly anadromous. On the other hand, the running of trout up the rivers to spawn is irregular, and most individuals are land-locked, as are also certain dwarf varieties of the salmon (as the Sebago salmon and the ouananiche of Saint John's River, Quebec).
Most trout, however, enter the sea when they can. These sea-run individuals often grow large and look like salmon, and, like the salmon, they enter the rivers to spawn. They do not, however, ascend the streams with as much energy, nor do they go as far, the instinct in these respects being much less perfect. To the large species entering the sea, intermediate in structure between trout and salmon, the name ‘salmon-trout’ is applied in England. The species so named (Salmo trutta) is considered by some as doubtfully distinct from the ordinary brown trout of Europe (Salmo fario). Other species which may be properly called salmon-trout, hav-
