Great Basin Naturalist


Examination of gastrointestinal tracts of native cyprinids from the Little Colorado River (LCR) in Grand Canyon, Arizona, 1990–1994, revealed varying rates of prevalence and infrapopulation levels of Asian tapeworm (Bothriocephalus acheilognathi). Mean prevalence was 28% (range 0–78%) in humpback chub (Gila cypha) and 8% (range 0–46%) in speckled dace (Rhinichthys osculus), with infrapopulations as high as 46 and 28, respectively. We also note Asian tapeworm infection of nonnatives common carp (Cyprinus carpio), fathead minnow (Pimephales promelas), and plains killifish (Fundulus zebrinus) from the LCR. Reported pathogenic and chronic effects of this cestode to its definitive hosts add concern for the status of the Grand Canyon population of the federally endangered humpback chub. The rapidity which Asian tapeworm has spread to different drainages of the Colorado River Basin likely portends an eventual cosmopolitan basin distribution in lower elevations suitable to the parasite's thermophilic life history. Such biotic changes must be considered among the most serious threats to conservation and recovery of native fish populations.