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Reintroduction concerns Hybridization For successful reintroduction ofbonytail into the UCRB, potential hybridization with humpback and roundtail chubs must be addressed. Evidence indicates that hybridization takes place to some degree in the wild between these closely related congeners (Holden and Stalnaker 1970). Vanicek and Kramer (1969) suggested that during spawning periods, spatial not temporal mechanisms separate bonytail from other Gila species. Kaeding et al. (1990) also believe that the isolating mechanism is spatial, based on their sampling protocol and studied design. Hamman (1982) was able to artificially produce a viable offspring from bonytail x roundtail chub crosses and bonytail x humpback chub crosses. However, these crosses did not occur in a hatchery environment without being induced. Although hybridization may be a natural part of the evolutionary history of the Gila complex, a successful reintroduction (as defined by the Recovery Program) can only occur if at least some bonytail can remain isolated until the population is stable. Nonnative fish interactions Successful bonytail reintroduction also requires minimizing impacts from nonnative fishes. Unfortunately, these impacts have only been minimally assessed to date. An in-depth understanding of community dynamics would allow a more effective reintroduction effort (Chart and Cranney 1993). Besides competing for resources, nonnative fishes exert pressure as predators. Low numbers of wild bonytail may be the reason nonnative predation on bonytail has not been documented. However, nonnative predation on humpback chub, tlannelmouth sucker and other native fish has been confirmed in the Colorado River system and should be considered as contributing to past and future losses of bonytail (Marsh and Douglas 1994; Valdez and Ryel 1995). Practical methods of minimizing predation impacts through theoretical modeling of gape limitation theory were examined by Alder and Crowl (1995). Using known predator size distributions within the upper Colorado River basin, it was theorized that bonytail are beyond most existing predation risk at 150 mm total length. This became the basis for the ideal stocking length for bonytail released into the basin. Although this may alleviate much of the predation risks for stocked bonytail, their progeny will still face the growing problem of nonnative predators. Conditioning: of hatchery fish It has been demonstrated that fish reared in captivity can become domesticated with respect to physiological parameters (Wiley et al. 1990). These effects may be minimized through shortened captivity (Nehring 1991). However, prolonged rearing may be necessary to grow bonytail to the recommended stocking size. Therefore, physical and behavioral conditioning of young bonytail before release has been considered as a potential strategy for minimizing the effects of domestication (Meyer 1992; Chart and Cranney 1993). Laboratory experiments were conducted 2