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Field tests.- No mortality or abnormal behavior was noted in any of the 30 humpback chub removed from the Little Colorado River and treated in a Praziquantel bath at 1.5 mg/L for 24 h. Tapeworm infestation in humpback chub from the Little Colorado River was highly variable. Small humpback chub ~ 150 mm TL) had few tapeworms but juvenile and adult humpback chub infestation was highly variable from 0 to 183 worms per fish (Figure 1). Tapeworm infestation appeared to increase dramatically in fish >200 mm TL. Discussion Commonly used low dosages ofPraziquantel (0.7 mg/L) are inadequate to remove 100% of Asian tapeworm. Although tapeworms are removed at these dosages some tapeworms commonly survive treatment within the host (Table 3&4). The minimum effective dosage is 1.5 mg/L and minimum effective duration of treatment is 24 hrs. Even at very high dosages (36 mg/L) one bonytail still had 3 live tapeworms after a 24-h treatment (Table 4). This indicates that even at high doses, Praziquantel bath treatments may not be 100 % effective at removing tapeworms. In heavily infected fish some tapeworms may not be exposed to the drug and survive treatment (Mitchell 2004). Fish that are being treated prior to translocation into areas where Asian tapeworm is not present should probably be treated multiple times to ensure no tapeworms survive treatment. No more than 65g offish per liter of water should be used in bath treatments (UDAF 1987) because fish density has been documented to impact treatment effectiveness (Mitchell 2004). Fish biomass loads during our tests were all below Ig offish per liter of water so it is unlikely that fish densities affected our results. Mitchell (1995) indicates higher dosages of Praziquantel and shorter holding times may be equally effective at removing tapeworms. Our results show some evidence that higher dosages of Praziquantel do lead to slightly faster evacuation of tapeworms. It is likely that this is