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Parasites of Native and Non-native Fishes of the Lower Little Colorado River, Arizona - 2000 Annual Report Hawaiian slings were used to collect channel catfish Ictalurus punctatus and common carp observed from shore. Snorkeling with this gear has been used to effectively capture channel catfish in the LCR under clear water conditions (Arizona Game and Fish Department, unpublished data). However, conditions during 2000 were not sufficiently clear to snorkel and spear guns were used only to capture fish observed, from above, near shore. We attempted to capture at least ten individuals of each species in each reach. Fishes collected for necropsy were limited by species: no humpback chub >150 mm could be necropsied and no more than five bluehead or t1annelmouth suckers> 150 mm could be sacrificed from each reach / trip. As many as 200 speckled dace or non-native species could be collected on each trip. The utility of these common fish as surrogates for monitoring parasite abundance in humpback chub will be examined. All fish captured were measured for total length (mm), weighed (g) and examined for external parasites (Lernaea cyprinacea). Fish not collected for necropsy were released alive at the site of capture. Necropsied fish were examined for parasites in the gastrointestinal (GI) tract, eyes, brain, kidney, liver, gall bladder, musculature and gills. Parasites were identified, counted, preserved and their maturity and attachment location in/on the fish recorded. Blood smears were also made, air-dried and preserved in 100% methanol and later stained with Giemsa to examine for blood parasites. Results A total of 6425 fish were captured (Table 1) and 805 fish were necropsied for internal parasites during the three trips (Table 2). Eleven species of fish were examined, including all four native species and seven non-native species (channel catfish, common carp, fathead minnow, plains killifish Fundulus zebrinus, rainbow trout, red shiner Cyprinella lutrensis and yellow bullhead Ameiurus natalis). Fifteen species of parasites were recovered (Table 3): four Nematoda, three Cestoda, three Monogenea, one Trematoda, two Myxosporea, one Copepoda, and one Acarina (the Acarina are most likely ectocommensal, not obligatory parasites). Channel catfish, humpback chub and speckled dace were the most highly infected fishes. Parasite species richness was highest in channel catfish, with eight species (Myxosporea, Cleidodiscus sp., Ornithodiplostomum sp., Corallobothriumfimbriatum, Megathylacoides giganteum, Bothriocephalus acheilognathi, Eustrongylides sp. and Contracaecum sp.), followed Hoffnagle et al. 2000 3