We tested the effect of predation by rainbow troutOncorhynchus mykisson the behavior and spatial distribution of Little Colorado spinedaceLepidomeda vittata, a native cyprinid that occurs in disjunct populations in northern Arizona. Field experiments demonstrated high predation on Little Colorado spinedace even in the presence of natural refuges and abundant macroinvertebrate prey. Little Colorado spinedace showed almost no predator avoidance in the presence of rainbow trout, which implies limited interaction with large nonnative predators through evolutionary time. Results suggest that rainbow trout may have a significant influence on the habitat use, behavior, and geographic distribution of Little Colorado spinedace, and may be responsible, in part, for the disjunct geographic distribution of this threatened native fish species.