Classification of the Native Trouts of Arizona with the Description of a New Species, Salmo apache

Abstract

A new species of trout, Salmo apache, is described from the White Mountains of eastern Arizona, in the Gila and Little Colorado River drainages. Specimens collected in 1873, 1915, 1937, and 1950, along with reliable information on trout introductions and study of collections made in the last decade, assure that certain stocks still persisting today are pure. Survival of the species has been greatly aided by the foresight of the White Mountain Apache Tribe. A second trout, Salmo gilae Miller (described from New Mexico), was also native to Arizona (as shown by 1888-1889 material from Oak Creek) but was eliminated after 1900. Salmo apache is distinguished by a set of characters involving life colors, spotting, body proportions, numbers of scales, vertebrae, and pyloric caeca, occasional presence of basibranchial teeth, and by its karyotype (2n = 56). It is compared with Salmo chrysogaster (of Mexico), S. clarki, S. aguabonita, S. gilae, and S. gairdneri, with some osteological observations included. Chromosomes show promise for helping to determine relationships in the genus Salmo, although much more data are needed. Speculations are presented on the origin of the trouts of Arizona, with information on an important Mexican fossil (Plio-Pleistocene) that may be closely related to S. chrysogaster. I conclude that the latter species represents a distinct phyletic line of Salmo, evidently the most primitive one in western North America, and that there are at least three other evolutionary lines. It is suggested that the California golden trout was derived from an ancestor (or combination of ancestral forms) that entered the Sacramento-San Joaquin Valley from the north, where it is perhaps represented today by the redband trout of McCloud River basin, California.