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Preliminary Testing of the Role of Exercise and Predator Recognition for Bonytail and Razorback Sucker By Gordon A. Mueller and Jeanette Carpenter, U.S. Geological Survey, and Robert Krapfel and Chester Figiel, U.S. Fish and Wildlife Service Summary Hatchery-reared juvenile, <25-cm TL (total1ength), razorback suckers appeared curious and showed no sign of predator avoidance when initially placed with large (>45-cm TL) flathead catfish. Predator-naIve juveniles (20- to 25-cm TL) exhibited no discernable preference when provided areas with and without (52 percent and 48 percent, n = 16 observations; 46 percent and 54 percent, n = 20 observations) large flathead catfish. However, once predation occurred, use of predator-free areas nearly doubled in two trials (36 percent and 64 percent, n = 50 observations; 33 percent and 67 percent, n = 12 observations). A more stringent test examining available area indicated predator-savvy razorback suckers used predator-free areas (88 percent, n = 21) illustrating predator avoidance was a learned behavior. Razorback suckers exercised (treatment) in water current (<0.3 mls) for 10 weeks exhibited greater swimming stamina than unexercised, control fish. When exercised and unexercised razorback suckers were placed together with large predators in 2006, treatment fish had significantly fewer (n = 9, z = 1.69, P = 0.046) mortalities than control fish, suggesting increased stamina improved predator escape skills. Predator/prey tests comparing razorback suckers that had been previously exposed to a predation event with control fish, found treatment fish also had significantly fewer losses than predator- naiVe fish (p = 0.017). Similar tests exposing predator-savvy and predator-naIve bony tail with largemouth bass showed a similar trend; predator-savvy bony tail suffered 38 percent fewer losses than control fish. However, there was not a statistically significant difference between the test groups (p = 0.143) due to small sample size. All exercise and predator exposure trials increased the survival rate of razorback sucker and bony tail compared to untreated counterparts. Introduction Historically, fish culturists have based production on the most economical method of raising large numbers of fish. In other words, the most fish for the fewest dollars. Traditionally, survival has not been an issue with recreational species, which are typically stocked to augment depleted communities. However, in endangered repatriation programs, fish are not only being stocked into altered habitats, but ones that are already at full carrying capacity. Natives not only have to avoid predation, but also have to out-compete resident fishes for food and space. The practice of mass stockings to augment imperiled fishes has proved problematic worldwide (Philipp art, 1995). Since 1980, more than two-million bony tail (Gila elegans) and 15-million razorback sucker (Xyrauchen texanus) have been reintroduced into the Colorado River basin (unpublished data, U.S. Fish and Wildlife Service, Dexter National Fish Hatchery). Unfortunately, survival has been extremely low (< 1 0,000), if not totally absent (Marsh and others, 2005). Marsh and Brooks (1989) reported that entire truck loads of hatchery razorback suckers were eaten by resident catfish within hours of release. Recent