Historically widespread and abundant throughout warm water reaches of the Colorado River basin, the endemic razorback sucker (Xyrauchen texanus) is now rare and listed as endangered (United States Fish and Wildlife Service, 1991). Mainstem dams that alter habitat and introduction of non-native fishes which prey upon or compete with early life stages are among the large-scale ecological disturbances that have negatively affected the razorback sucker (Tyus, 1987; Minckley et al., 1991). Rarity of larval and especially juvenile razorback suckers in collections, and presence of only aged adults in remaining populations indicates recruitment failure (McCarthy and Minkley, 1987; Lanigan and Tyus, 1989; Minckley et al., 1991). Adult razorback [...]