Fish communities that share an evolutionary history typically have mechanisms to offset impacts presented by other species. Fish, especially non-game species, which are intermingled with non-native species for which they lack a shared history, are often poorly adapted to offset these impacts. Non-native fish affect native fish through predation, competition, displacement, and disease, affects which are often synergistic. Native fish within the Muddy River system (Clark County, Nevada) experienced a precipitous decline in numbers following an illegal introduction of blue tilapia (Oreochromis aureus) during the 1990\u27s. The purpose of this investigation was to determine if tilapia were directly predating upon fish, which is a phenomenon not substantially reported in scientific literature but possible, for example, due to contemporary evolution. In addition if piscivorous, various factors including gender, health, size, and habitat were examined to ascertain influence over predation. This information would inform management of the fisheries resources in the Muddy River and throughout Southern Nevada. Tilapia were collected at both the Nevada Power Reid Gardner generating facility and the Muddy River, and stomach contents were investigated. Blue tilapia were determined to be piscivorous, which was weakly related to gender, habitat, and body length. Muddy River populations, which were predominately male, more frequently had fish in their digestive systems than did tilapia from the Reid Gardner ponds. Body condition of tilapia was not related to piscivory. Due to the weakness of the relationships, additional study is warranted, including information on other habitat variables. This investigation underscores the importance of a tilapia removal program for waters in Southern Nevada. A management plan and invasion framework was proposed to address the problem
