Invasive species threaten biodiversity worldwide. Armored catfish, which are benthic grazers, have been introduced globally and damage ecosystems in numerous ways. However, their competitive interactions with native benthic grazers have not been tested. This study tested for the effects of an invasive armored catfish (Hypostomus plecostomus) on performance in native Rio Grande leopard frog (Rana berlandieri) tadpoles. Aquarium tests showed that armored catfish can negatively affect native amphibian survival and growth even when food is abundant. However, mesocosm tests showed no effects or competition. While the mechanisms of effect remain unclear this is the first study to demonstrate exotic armored catfish as a potential threat to native amphibians, which are declining globally.