ASIAN TAPEWORM (BOTHRIOCEPHALUS-ACHEILOGNATHI) IN NATIVE FISHES FROM THE LITTLE-COLORADO RIVER, GRAND-CANYON, ARIZONA

Examination of gastrointestinal tracts of native cyprinids from the Li ttle Colorado River (LCR) in Grand Canyon, Arizona, 1900-1994, reveale d varying rates of prevalence and infrapopulation levels of Asian tape worm (Bothriocephalus acheilognathi). Mean prevalence was 28% (range 0 -78%) in humpback chub (Gila cypha) and 8% (range 0-46%) in speckled d ace (Rhinichthys osculus), with infrapopulations as high as 46 and 28, respectively. We also note Asian tapeworm infection of the nonnatives common carp (Cyprinus carpio), fathead minnow (Pimephales promelas), and plains killifish (Fundulus zebrinus) from the LCR. Reported pathog enic and chronic effects of this cestode to its definitive hosts add c oncern for the status of the Grand Canyon population of the federally endangered humpback chub. The rapidity with which Asian tapeworm has s pread to different drainages of the Colorado River Basin likely porten ds an eventual cosmopolitan basin distribution in lower elevations sui table 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.