The Dolly Varden, or bull-trout, belongs to a different genus (Salvelinus), and is related to the brook trout of Eastern waters, having also red spots. While the red-throat trout inhabits both slopes of the Rockies, the others named belonged originally to the Pacific Slope.
The Red Throat Trout (Salmo clarkii)
The red-throat trout is the most widely distributed of the Western trouts. It inhabits both slopes of the Rocky Mountains, and, as might be inferred from this extensive range, it varies in external appearance more than any of the trout species. There are a dozen or more well-defined sub-species or geographical varieties, but all have the characteristic red splashes on the membrane of the throat. By means of this "trademark" it may be readily distinguished from the rainbow or steelhead trouts, both of which are also black-spotted.
Nomenclature
But while the red-throat trout varies considerably in contour, coloration and markings, in different localities, it is identical in structure wherever found. It is known by the United States Bureau of Fisheries as the "black-spotted trout," a most unfortunate designation, inasmuch as the rainbow and steelhead trouts are also "black-spotted." The name red-throat is distinctive, and is preferable to the rather repulsive name of "cut-throat" trout by which it is also known. The red-throat trout is designated in its native waters by such names as "trout," "brook trout," "speckled mountain trout," etc. As the Eastern red-spotted "brook trout" is rapidly being introduced to Western waters, the name "brook trout" should be applied only to that species.
Growth and Weight
Where the red-throat trout grows to a larger size than usual, as in the Yellowstone and other lakes, it is often called "salmon-trout," and the bull-trout of the Pacific Slope is also sometimes known by the same name, but the only "salmon-trout" is the steelhead trout. The red-throat trout rises to the fly more freely than the Eastern brook trout, though in gameness and flavor it is hardly its equal. Its habits are also somewhat different. It usually lies in pools and holes, and does not frequent the riffles so much as the Eastern trout. In size it is somewhat larger than the Eastern trout in streams of the same relative width and depth, and like all trout species grows to greater weight in lakes and large streams. I have taken them on the fly weighing from three to five pounds in Soda Butte Lake in the Yellowstone Park, and in Yankee Jim Cañon on the Yellowstone River. In Yellowstone Lake some are infested with the white pelican parasite, rendering them emaciated and lacking in game qualities; this condition, however, seems to be disappearing somewhat, while those in the river below are well-nourished and gamy.
Tools and Tackle
The same tackle and artificial flies used for the Eastern brook trout are as suitable, as a rule, for the red-throat, though preference is given to the stone fly, coachman, professor, black gnat, cinnamon, Henshall, and the various hackles by Montana anglers. The red-throat seldom breaks water when hooked, but puts up a vigorous fight beneath the surface. As the mountain streams are usually swift and rocky and fringed with alders, willows and other small trees, the angler must be wide awake to land his fish and save his tackle.
The Steelhead Trout (Salmo gairdneri)