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Changing Fish Fauna of the Southwest 377 6 1925, p. 342). The speckled dace, Rhinichthys osculus (Girard), was perhaps eliminated chiefly by rising water temperatures as the river became deeply entrenched, the vegetation was destroyed, and the water supply shrank. The flow diminished so markedly between 1939 and 1950 that even the two exotic species, the black bullhead (Ictalu- rus melas Rafinesque) and the green sunfish (Lepomis cyanellus Rafinesque), had disappeared here, presumably because of insuffi- cient cover. On June 22, 1959, the river was dry at Benson, and only damp at St. David and Fairbank. SALT RIVER (TABLE III) The shift from 11 native species to 5 exotic species in the Salt River south of Phoenix, during approximately a half century, reflects changing water conditions upstream (dam construction, irrigation) and the establishment of exotics. Before the turn of the century the river was of sufficient size and flow to support such big-river or cur- rent-loving fishes as the roundtail (Gila r. robusta Baird and Girard), bonytail (G. r. elegans), woundfin (Plagopterus), flannelmouth sucker (Catostomus latipinnis), and humpback sucker (Xyrauchen) ; overflow, marshlike areas presumably provided habitats for the pup- fish and topminnow (Cyprinodon and Poeciliopsis). As the river dwindled in volume and depth to a comparatively shallow stream dominated by shifting sand, longfin dace (Agosia) appeared and at- tained numerical superiority, and Gala robusta intermedia Girard, a headwater and small-creek ecotype, appeared in place of the bonytail. With the desiccation of the river at this point by 1943, only predatory introduced species remained. Farther upstream in Salt River, at and near the present site of Roosevelt Dam, there were, in 1904, only 1 exotic species (the carp), and 10 native species including Colorado squawfish, spikedace (Meda fulgida Girard), flannelmouth and humpback suckers, and the Gila topminnow. By 1937, Meda had disappeared, the last adult squawfish was captured, the humpback sucker had vanished, and Poeciliopsis had been eliminated. The bigmouth buffalo (Ictiobus cyprinellus), yellow bullheads, bluegills, yellow perch, and yellow bass had become established-a total of 7 native and 6 exotic species. In 1950, the reservoir contained only 8 introduced fishes, although near its head Salt River still supported 6 native species, including roundtails, 11