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Abstract. - Asian tapeworm (Bothriocephalus acheilognathz) is potentially fatal to multiple age classes of fish, and can cause high mortality when infecting new host species. The spread of Asian tapeworm has been identified as a potential threat to endangered cyprinid fish such as humpback chub (Gila cypha). Field investigations to quantify tapeworm loads previously required fish to be killed and dissected so sample sizes were small and few adult fish were examined. The advantage of using Praziquantel to evaluate parasite loads is that it does not require killing fish, allowing monitoring of tapeworms in rare fish species that cannot be sacrificed. We used bonytail (Gila elegans) as a surrogate for humpback chub and performed laboratory experiments to evaluate the dosage and time needed to effectively remove 100% of Asian tapeworm using Praziquantel. Treatments less than 24 hours were not effective at removing all tapeworms even at high doses (36 mg/L). Commonly used dosages (< 0.7 mg/L) were ineffective at removing 100 % of tapeworms. No mortality or side effects ofPraziquantel treatment were observed. Tapeworm loads in rare fish can be accurately quantified in the field without dissection, provided that adequate water quality can be maintained in a treatment container for a 24-hour period. We used this method to evaluate tapeworm loads in 30 humpback chub from the Little Colorado River in May of2005. Tapeworm infestation was highly variable (0-183 per fish) and probably linked to river hydrology. Continued monitoring is needed to evaluate tapeworm infestation and impacts on humpback in the Little Colorado River. Introduction Asian tapeworm (Bothriocephalus acheilognathi) has been identified as one of six potential threats to the continued persistence of humpback chub (Gila cypha) (USFWS 2002). Asian tapeworm was first documented in the Little Colorado River (LCR) in Grand Canyon in 1990 (Minckley 1996), and has subsequently been found in most of the cyprinid fishes inhabiting the Little Colorado River (LCR) (Cole et al. 2001). It is considered one ofthe most dangerous cestodes of cultured carp in Europe, and can cause heavy infections in juvenile cyprinids especially when spreading into new locations (Heckmann and Deacon 1987). When parasites are numerous, marked enlargement of the abdomen can occur with severe hemorrhagic enteritis and intestinal blockage (Hoole and Nisan 1994). Asian tapeworm is potentially fatal to multiple age classes of fish (Schapperclaus 1986), and causes high mortality when infecting new host species (Hoffman and Schubert 1984). Parasitized carp in hatcheries cease feeding, become emaciated (Hoole and Nisan 1994) and die with up to 100% losses (Korting 1975).