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Impacts of introduced fishes (reviewed by Taylor et al 1984) are seldom understood, and largely inferred from major alterations of species composition in an area. Competition (reviewed by Connell 1983, Ross 198b) between native and introduced forms is difficult to observe experimentally, and perhaps impossible to prove in natural riverine habitats. Direct effects of fish introductons on native fishes were categorized and reviewed by Moyle et al (1981): Elimnination, reduced growth and survival, changes in community structure, and no effect. These authors stressed that many fish are introduced (~ into habitats that are also changiag due to the effects of man, making it ~~i difficult to determine if habitat change, competition, or both, are responsible for decline of the natives. To confound this already complex issue, in the past, species interactions were not well understood, and never studied before introductions were made. Introductions of new species into areas to promote better sport fishing has often created more problems than solving them, primarily because methods for predicting outcomes are few (Li and Moyle 1981). The introduction of non-native fishes in the Colorado River has been documented by many, and present status provided by Minckley (1982) and Tyus et al. (1982a). The impacts of these introductions on decline of the Colorado squawfish remains problematic, differing among life stages, temporally and spatially: Larvae- Small Colorado squawfish are eaten by other fishes, and probably compete with young of other species as well. Study of predation upon small larval Colorado squawfish is difficult because the fragile larvae may be 32