Asian tapeworm Bothriocephalus acheilognathi, a parasite known to be pathogenic to cyprinid fishes, is established in San Bernardino National Wildlife Refuge, southeastern Arizona, USA. The San Bernardino refuge is home to endangered Yaqui chub Gila purpurea, and Yaqui topminnow Poeciliopsis occidentalis sonoreinsis, and our experiment measured the effects of Asian tapeworm on the growth and mortality of these species. Our experiment employed forty 75.8-L aquaria, with 10 different treatments, each having 4 replicates. We stocked fish at 2 single species densities and 1 mixed species density to see if competition has an impact on infection effects. We found a significant difference between growth rates of Yaqui chub that were exposed to Asian tapeworm and those that were not. We did not find a difference between the growth rates of Yaqui topminnow, nor did we find a difference in the mortalities of between exposed and unexposed tanks. This information was published in an MS thesis and is currently being compiled for journal publication.