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Could Exercise Conditioning Increase the Success of Repatriation Efforts for Colorado River Fishes? Ward, David L. 1, and Kara D. Hilwig2 'Arizona Game and Fish Department, Research Branch, Phoenix, AZ; 2Northern Arizona University, Department of Biological Science, Flagstaff, AZ Rare native fish are often reared at hatcheries in ponds or tanks for later stocking into streams with depleted populations. Fish reared in standing water may experience increased stress, downstream displacement, or high predation mortality when released into lotic environments. We compared the swimming performance of captive fish held in standing water, captive fish exercised in flowing water, and wild fish captured from a stream, to evaluate the effects of exercise conditioning and holding environment on swimming performance. Swimming performance of flannelmouth sucker Catostomus latipinnis, bonytail chub Gila elegans, razorback sucker Xyrauchen texanus, and spikedace Meda fulgida held in standing water increased by 10, 15, 26, and 40% respectively after exercise conditioning in flowing water (10 - 100 cm/s) for as little as 10 d. Exercising fish reared in standing water may improve swimming performance and increase survival. Lake Mohave Razorback Sucker Program Update Tom Burke Bureau of Reclamation, Boulder City, NV During the late 1980's over 90% of the wild, adult razorback sucker population left in the world, roughly 63,000 fish, resided in Lake Mohave. Despite annual spawning along the lake's shoreline, natural recruitment of new fish into the population was almost nonexistent due to predation from non-native fishes. Razorback suckers live about 40-45 years, and Lake Mohave was formed in the early 1950's. These fish were slowly dying of old age. Without help, this population was expected to die off around the turn of the century. The Native Fish Work Group began working in 1991 to replace this stock with its own offspring. The NFWG is a team of fishery biologists representing Arizona Game and Fish, Nevada Division of Wildlife, National Park Service, Arizona State University, Southern Nevada Water Authority, Fish and Wildlife Service and Bureau of Reclamation. The team collects young fry from the early spring spawning and transfers them to a local hatchery where they are raised to approximately 4 inches. The young fish are then moved to lakeside ponds or other hatcheries for further rearing. When the fish reach 12 inches in length, they are tagged and released into the main body of the reservoir. The Native Fish Work Group's goal is to build up the spawning population to 50,000 adult fish. To date, over 75,000 juvenile fish have been repatriated to the lake, and an additional 120,000 are at some stage of rearing to target release size. An overview of program methods are presented along with results to date. 16 1 1 1 1 1