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MINNOW FAMILY, CYPRINIDAE 195 and ~d color to Sacramento o the rest of the body, ate 9 rays in the dorsal d the pharyngeal teeth ~g to the superficial Jordan and Evermann ~rado" or "whitefish." r River and its major ~lorado River and rare ~troduced. 's. The large adults are er and in large pools of edge or shallow pools Sacramento squawfish, occurs naturally in the than SO mm TL feed :. Aquatic insect larvae mm TL, while fish, rater than 100 mm TL mm TL feed almost Kramer found that 39 empty. ~civore in a major river ermann (1896) indicate this species the largest than 18 kg have been tamer (1969) collected o squawfish, Colorado population studied by year II, 162 mm TL at After the fifth year, the U. Vanicek and Kramer river below a new dam y because the tempera- warmer on the average zing takes place in July l on water temperatures :end Kramer, 1969). In filer and Miller, 1963). undoubtedly similar to is some evidence that Colorado squawfish may once have made extensive spawning migrations (Sigler and Miller, 1963; Di11,1944), which have now been blocked by dams. Status. Colorado squawfish were once very abundant in the lower Colorado River (Minckley, 1973) but by the early 1960s they were probably extinct there. They are raze enough elsewhere to be regarded as an endangered species (Leach et aL, 1974). Their disappearance is most likely the result of the drastic changes in the nature of the Colorado River, caused by large dams built in recent years. Neither the extensive reservoirs behind the dams nor the cold, clear water that flows from them provides the habitat necessary for squawfish survival. In addition, the dams block spawning and migration, curtailing reproduction. In the waters flowing from Flaming George Dam on the Green River, Vanicek (1970) found that Colorado squawfish, along with other native fishes, have been replaced by rainbow trout. In areas where squawfish still survive their growth rate is reduced and large fish are rare. Vanicek and Kramer (1969) listed several factors besides habitat change which might have caused this: competition from introduced channel catfish; death from having channel catfish, with erect fin spines, lodged in their throats; overexploitation byfishermen; and an excessively heavy load of exotic parasites acquired from introduced fish species. It is unlikely that breeding populations of Colorado squawfish will ever become reestablished in the California portion of the Colorado River as long as the present water conditions persist, although attempts are now being made to breed them in the Willow Beach Hatchery, Arizona, in order to reintroduce them to the river (S. Nicola, pers. comm.). It can only be hoped that other states that still possess stretches of river suitable for this fish will preserve these areas in their natural state. The best such remaining stream for this purpose is the lower Yampa River, Colorado (Holden and Stalnaker, 1975). References. Dill, 1944; Jordan and Evermann, 1896, 1923; Holden and Stalnaker, 1975; Leach et al., 1974; Sigler and Miller, 1963; Vanicek, 1970;. Vanicek and Kramer, 1969. Speckled Dace, Rhinichthys osculus (Girard) Systematic Note. No freshwater fish in the western United States is as widely distributed or occupies such a wide variety of habitats as does the speckled dace. Its adaptability is reflected in its variability and many distinct forms of it exist. Jordan and Everman (1$96), for example, divided the complex into twelve species. Although systematists now seem to have little trouble placing the many forms into Rhinichihys osculus (Hubbs, Miller, and Hubbs, 1974), the status. of the many described (and Figure 65. Speckled dace, 7.4 cm SL, Sagehen Creek, Placer County.