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Inbreeding depression is a reduction in fitness associated with the partitioning of deleterious alleles in the homozygous condition (Lande 1995). However, the result of ongoing inbreeding-depression is a purging of deleterious alleles, and over time, an increase in population fitness (Lynch et al. 1999). Genetic data generated in RBS broodstock development will allow managers to preclude the mating of related individuals (Blouin et al. 1996; Norris et al. 2000), and prevent both inbreeding and inbreeding depression. Outbreeding and outbreeding depression Outbreeding is the sexual combination of divergent genomes. Extreme outbreeding results in developmental instability, and is often associated with sterility, particularly in the heterogametic sex. Mules are an example of outbreeding. Outbreeding depression occurs when the offspring have a reduced fitness because of the combination of diverse genomes. Outbreeding depression can occur in the first generation by affecting the adaptation to fine scale environmental conditions. Loss of local adaptation will result in a decrease in the overall fitness of the population. Outbreeding depression as a result of hybrid breakdown occurs in the second generation, when recombination produces a montage of maladaptive progeny (Burton 1990). Loss of population diversity or loss of population identity occurs in a captive propagation program when different populations are mixed and interbreeding occurs. Outbreeding is fundamentally as significant a problem as inbreeding (Burton 1990). The RBS population in Lake Mohave is predicted to be a sump for inundated populations throughout the basin. If this is true, then outbreeding is an ongoing process occurring in every spawning aggregation and not a major concern in controlled propagation programs. Domestication/artificial selection in captive populations Genetic variation of captive populations can be altered on a hatchery when the 26