The rainbow trout is the only species of trout native to the waters of Yosemite National Park, all other kinds having been introduced. Originally it was found in the Merced and Tuolumne river systems below the high, free-leaping waterfalls which limited their upstream migration to Yosemite and Hetch Hetchy valleys.

The most gamy of trout, rainbow after being hooked will often exhibit aerial acrobatics—leaping high into the air time after time. It is an excellent fly fish, striking readily at feathered lures from the early summer on, after the streams and lakes have begun to lose their springtime volume.

This species may be distinguished by the uniform, tiny black spotting on its sides and back plus the rose-colored band extending the body length along either side.

The rainbow is one of the most adaptable of all trout. The hardiness is most apparent in streams where it is present with other kinds of trout. In Yosemite, the rainbow may thrive in certain places where species such as the eastern brook trout appear thin and unhealthy. This may be due to the fact that the rainbow seems to be able to forage for food more successfully than other species.

An intricate set of conditions keeps a trout in balance with its environment. Fluctuations in volume and temperature of water, lack of food, pollution, abundant predators, disease, and lack of shelter or spawning areas are just a few of the factors which make trout necessarily highly adaptive creatures. For its splendid survival under a variety of conditions and also since it is the native species in Yosemite, most emphasis in artificial propagation and planting is placed on the rainbow. It has been planted under the names of Shasta trout, McCloud River rainbow and steelhead trout. All of these forms are quite similar and it is difficult to distinguish one from another.

Rainbow trout spawn in the spring from March to June on a rising temperature depending upon the locality and the water temperature. In some of the high mountain waters they have been observed to spawn as late as midsummer. At spawning time, they tend to move upstream and seek the smaller tributaries, or in the case of those inhabiting lakes, inlets are utilized. The eggs hatch in about fifty days.

From the Merced River in the floor of the Valley up to high alpine lakes, this species is found. The rainbow is characteristic of the swifter, white water of the streams like that in the Merced canyon below the valley. In size it is somewhat limited, as even lake specimens are rarely caught which weigh more than three pounds. Nevertheless, it is more valuable from the sportsmen’s standpoint than any other trout in the park and is much sought after wherever it becomes established.

The local form is referred to scientifically as Salmo gairdnerii irideus, which name is used for the wide-spread, generally nonmigratory, moderately coarse-scaled, relatively deep-bodied, big-headed and big finned type. The Yosemite form has been referred to as “Salmo shasta,” the Shasta rainbow trout of fish culturists, but recent examination at Sanford University of the type specimens of Salmo g. shasta Jordan by Dr. Carl L. Hubbs and Dr. W. I. Follett, ichthyologists, failed to disclose any valid reason for even the sub-specific recognition of shasta.

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