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The salmons are soft-rayed fishes with no spines in any of the fins, with the ventrals situated on the abdomen far behind the pectorals, and with a fleshy rayless "adipose" fin on the back behind the rayed dorsal fin. The presence of this adipose fin, and its situation, separates them from all other Gulf of Maine fishes except for the smelt, capelin and the argentine, the pearlsides (p. 144), and some of the lantern, viper, and lancet fish tribes (p. 141).[44] The blunt noses, stout bodies, and nearly square tails of the salmons distinguish them at a glance from the sharper-nosed, slender, forked-tailed smelts, their large mouths and smaller eyes from the argentine; the absence of luminescent organs distinguishes them from the [page 120] pearlsides, while the lantern, viper, and lancet fishes are of different general aspect.

Four salmons[45] occur in the Gulf of Maine, or have recently, one of which, the sea trout, resorts to tidal estuaries at the mouths of a few of our streams; a second and a third-the humpback salmon and the silver salmon-were introduced from the Pacific coast, leaving the Atlantic salmon as a characteristic inhabitant of the open waters of the Gulf of Maine.

1. Scales so small that they are hardly visible; back with vermiculate markings; teeth on roof of mouth confined to a group in front Brook trout, p. 120
Scales large enough to be easily visible; back without vermiculate markings; a row of teeth runs back along the mid line of the roof of the mouth 2  
2. Anal fin with only 8-10 rays Salmon, p. 121
Anal fin with 12 rays or more 3  
3. Back and lower half of tail fin, as well as its upper half, conspicuously marked with large black spots Humpback salmon, p. 131
Back with very small black spots or none at all; no black spots on lower half of tail fin Silver salmon, p. 133

[44] Sundry other deep-sea fishes have adipose fins.

[45] A specimen of one of the whitefishes (probably Coregonus quadrilateralis Richardson) was taken in the mouth of the Sissibou River, St. Mary Bay, Nova Scotia, September 1919 [Huntsman, Contr. Canad. Biol., (1921) 1922, p. 59] straying down from fresh water. Whitefish have an adipose fin, like the true salmons, but have a very small mouth, and are flattened sidewise, and herring-like in appearance, rather than salmon-like.