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1. Background. Low survival can be a major limiting factor during earl life stages. When recruitment does not replace adult mortality, wild stocks decline in numbers. For example, Colorado River squawfish and humpback chub stocks are considered to be low but stable in the upper basin. To protect these stocks and increase their numbers, fishways will be constructed to provide passage over dams into historic habitats. In addition, stream flows needed to maintain vital habitats for both species will be defined. Although spawning has been documented, recruitment of wild razorback suckers is low or non-existent. Therefore, attempts will be made to enhance flooded bottomland habitats with the goal of increasing survival during early life stages to aid natural recruitment. Evaluation of these sites as nursery areas may require stocking naturally spawned larvae into protected (predator-free) sites as recommended-by Dowling and Minckley (1993) in Lake Mohave. 2. Guidelines for Maintaining Genetic Diversity in Wild Larval Fish to be Stocked in Protected Environments. Larval fish should be collected from or near a known spawning site in a suspected historic nursery area. Temporal sampling of larvae should be made throughout the natural spawning period (Tyus and Karp 1991). For example, collections could be made weekly using light traps. An attempt should be made to collect equal numbers of larvae during each collection. Standardized techniques should be used during all collections so that mortality of larvae during capture and handling is similar among collections. Ideally, larvae from each collection should be marked. Batch-marking techniques for larval • fish are available through food additives but they require lethal sampling. 3. Genetic Characterization of Fish Produced in Protected Environments. If wild fish reared in protected habitats are genetically similar to the wild spawning stock, they can be reintroduced near the spawning site. The number should not exceed 10 per cent of the spawning population. All released fish must be identifiable by a unique mark or tag so they can be monitored in the future. If only a few larvae survive in the protected environment or the genetic characterization indicates that the surviving fish originated from only a few parents, the fish should not be stocked. Dispose of-such fish in accordance with guidelines in Section VI.B. D. Hybridization. Hybridization has important management and evolutionary consequences. Hybridization increases when allopatric populations are placed into sympatry through human activities and when sympatric populations inhabit altered environments (Both et al. 1987). No hybridization has been documented in the Colorado squawfish. However, hybridization has been documented for razorback suckers and the endangered Gila sp. in the Upper Colorado River Basin. Pallid sturgeon may be hybridizing with shovelnose sturgeon in the Mississippi River, and bull trout are known to hybridize 12 0