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Wild razorback sucker originally occupied habitat in the Upper Colorado River from about Rifle, Colorado, to the confluence with the Green River, and in the Gunnison River from approximately Delta, Colorado, downstream to the confluence with the Colorado River (Valdez et al. 1982; Holden et al. 1981; Burdick 1992; Burdick and Bonar 1997). In the Gunnison River, the last captures of wild razorback sucker were in 1981 when three adults were captured immediately downstream from Delta (Holden et al. 1981) (Figure 1). In the Upper Colorado River only a few individuals are thought to remain. Remaining wild individuals are composed exclusively of old adults. Populations of wild razorback sucker are now virtually extinct in these river reaches, and inadequate numbers exist in the wild to allow populations to be restored through natural reproduction or for natural recolonization and expansion to occur. Therefore, in the Upper Colorado and Gunnison rivers, too few adult razorback sucker now exist to maintain self-sustaining or to re-establish populations in the riverine system, largely believed to be due to persistent recruitment failure. Although limited recruitment may have been occurring, it was not sufficient to maintain populations in either river. In the Upper Colorado River Basin, razorback sucker larvae have been collected in the Green and Colorado rivers, but juveniles are essentially absent (Gutermuth et al. 1994; Muth et al. 1998; FWS 1998). Juveniles have been reported throughout the basin (Taba et al. 1965; Modde et al. 1996; Holden et al. 1997); however, their collection is extremely rare suggesting there is little or no recruitment to old, relic populations (Minckley et al. 1991; FWS 1998). Consequently, the Biology Committee of the Upper Colorado River Endangered Fishes Recovery Program (RP) placed a high priority on re-establishing razorback sucker in the Upper Colorado and Gunnison rivers by stocking domestically-produced and reared fish. Razorback sucker are considered a priority 1 species (Czapla 1999; Nesler et al. 2002) for augmentation and restoration efforts in Colorado (Kesler 2001) and Utah (Hudson 2001) due to the presence of, but declining trend of wild populations due to inadequate recruitment. There are five primary components to achieving recovery of razorback sucker and the other endangered fish species in the RP. One of these is propagation, stocking, and genetics management. Thus, propagation and stocking is considered one of the primary approaches to establishing self-sustaining populations. An effective stocking program for establishing razorback sucker populations would require that stocked fish: 1) remain in the system and successfully adapt to the habitat into which they are stocked, 2) ultimately survive to adulthood, mature, and contribute offspring that restore or increase the size of an existing population, and 3) present an acceptable risk to other native aquatic species and communities. Stocking is believed to provide 3