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47 catfish, bluegill, carp, and thread fin shad. Colorado squawfish stocked in the Verde River, Arizona, were preyed heavily upon by yellow bullhead (Hendrickson and Brooks 1989). Predation was suggested as a reason for local declines of roundtail chub in the Gila River drainage, New Mexico. Roundtail chub populations were rare in areas of syrnpatry with smallmouth bass, but were abundant in reaches without smallmouth bass (Bestgen and Propst 1989). There are three requirements for competition to occur between two species. The resource must be limited, it must be shared, and sharing must produce a negative influence on one of the species (Li 1979). Field documentation of competition was difficult Dietary or spacial habitat overlap has been documented but no studies have concurrently examined availability of the resource in question. Competition for food was implied by several studies that verified dietary overlap. Dietary overlap was confirmed by examination of stomach contents of Colorado squawfish and several exotic fishes. Overlap was identified most frequently with channel catfish and red shiner; other species with less strong overlap included fathead minnow, sand shiner, green sunfish, black bullhead, and carp (Jacobi and Jacobi 1981; McAda and Tyus 1984; Grabowski and Hiebert 1989; Karp and Tyus 1990b). No information was found that identified dietary requirements or overlap with razorback sucker, humpback chub, or bonytail chub. ' Introduced fishes may also provide forage for native fishes. Red shiner, common carp, or fathead minnow were identified as food sources for juvenile or adult Colorado squawfish, with red shiner the most predominate food item (Vanicek 1967; Jacobi and Jacobi 1981; McAda and Tyus 1984; Grabowski and Hiebert 1989). Channel catfish have been shown to cause some problems by lodging in the throats of Colorado squawfish (Vanicek 1967; McAda 1983; Pimentel et a1. 1985; Wick et al. 1985), but were not considered a major reason for decline because they were not preferred food items (Pimentel et al. 1985) and the number of squawfish found in this condition was relatively small (McAda 1983). Not all predation of channel catfish resulted in lodging injury (Pimentel et al. 1985). Spatial competition was suggested by habitat-use overlap of young Colorado squawfish, red shiner, sand shiner, and fathead minnow (Holden 1977; McAda and Tyus 1984; McAda and Kaeding 1989). Territorial defense aggression was exlubited by green sunfish, fathead minnow, and red shiner toward young Colorado squawfish in aquaria (Karp and Tyus 1990a). Competitive interactions were inferred by similar habitat use by adult Colorado squawfish and channel catfish, northern pike, and walleye (Wick et a1. 1985; Tyus and Karp 1989; Tyus and Beard 1990).