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Risk Assessment of Reintroduction and Augmentation Releasing hatchery-reared fish into areas that are populated with wild fish is not without risks. Potential risks associated with stocking have been identified (Busack 1990; Burdick 1992; Ryden and Pfeifer 1994; Ryden 1997) and strategies outlinrd to minimize negative impacts on wild razorback sucker populations. Genetic 1. Outbreeding depression: outbreeding depression results in the loss of fitness from crossing distantly related individuals. The Genetics Management Plan (Williamson and Wydoski 1994, Czapla 1999) recommends using local populations first (Green River stock), then nearest neighboring population (Colorado River stock), and lastly, using broodstock from the Lake Mohave population. Following the Genetics Management Plan protocol will reduce the risk of outbreeding. 2. Inbreeding depression: if razorback sucker stocked into the Green and Colorado rivers are too closely related to each other and they reproduce in the wild, their progeny could suffer detrimental effects (reduced fitness or death) from inbreeding. To reduce the risk of inbreeding depression, the recommended target breeding strategy for propagation of the endangered Colorado River fishes, as outlined in the Genetics Management Plan (Williamson and Wydoski 1994; Czapla 1999), is to mate 25 females with 25 males to produce 25 pedigreed family lots if sufficient adults are available. An inbreeding rate of 1% is estimated for an effective population size of SO fish which is acceptable for maintaining the genetic diversity of captive fish stocks used as founders (Williamson and Wydoski 1994}. 3. Hybridization: increased numbers of razorback suckers may result in hybridization with native flannehnouth and bluehead suckers and with nonnative white suckers. This could lead to a loss of interspecific genetic identity. Flannelmouth and razorback suckers hybridize in the wild (Huth et al. 1987) as do flannehnouth and bluehead suckers (Ryden and Pfeifer 1995) but hybridization rates are low. Stocking hatchery-reared razorback suckers is not expected to increase the rate of hybridization between these species of native suckers (Burdick 1992). Flannelmouth and bluehead suckers hybridize with the nonnative white sucker (Ryden and Pfeifer 1995; 1996a and 1996b). Razorback sucker may also hybridize with white sucker. This is not expected to be a significant problem. Ecological 1. Pathogen and parasite transmission: pathogens and parasites (i.e., Asian tapeworm) harbored by hatchery reared fish could adversely impact wild fish populations. A resistant broodstock may transmit pathogens into wild populations, which may have little or no resistance. To reduce the risk of pathogen and parasite transmission, inspections are conducted by the Fisheries Experiment Station (UDWR) to ensure that culture facilities and wild broodstock sources are specific pathogen free and meet the requirements of the Fish Health Policy Board. Those facilities which are pathogen free according to Hiles set forth by the Fish Health Board are given fish health 4