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June 1989 Marsh and Brooks-Ictalurid predation on Xyrauchen 193 and striped bass (Morone saxatilis) from nursery ponds into an adjacent reservoir. Osmundson (1987) similarly noted that stomachs of largemouth bass (Microp- terus salmoides) contained only newly-introduced Colorado squawfish (Ptycho- cheilus lucius) for several days after stocking, despite an abundance of other r forage species. Since 1981, more than 700,000 juvenile razorback suckers have been stocked into the Gila River and its tributaries (DNFH and AZGFD files). Despite intensive sampling effort, only 16 fish have been recovered as of April 1988, more than a few days after stocking in mainstream habitats. We believe predation impacts account in large part for apparent low survival of stocked fish, because the fish has high survival when placed, even as larvae, into predator-free habitats (Marsh and Langhorst, 1988; Marsh, in press). By extrapolating 1985 density estimates and observed rates of consumption of razorback suckers by catfishes, we estimated that the catfish population per kilometer of stream could have consumed about 900 razorback sucker of the sizes stocked in a 24-h period. Catfish occur at least 40 km downstream, and, because habitat changes little, catfish densities are presumably similar to those measured. Thus, downstream movements of stocked razorback suckers at night (J. E. Brooks, pers. obser.) probably exposed them to continuing predation. Given sufficient time, and assuming that predation rate did not change upstream to downstream in each study period, the razorback suckers stocked in 1984 (5,000 fish) could have been eliminated within 6 km of stream, and those of 1985 (25,875) in a little less than 20 km. However, the 4,600 razorback planted in 1986, when predation intensity was lower, would not have been removed until more than 37 km downstream, about six times the distance required for the similar number stocked in 1984. Nonetheless, this last fact is far from encouraging as regards successful reintroduction of small razorback suckers. Although this study involved stocked razorback suckers generally less than 150 mm, the relationship between predator and prey sizes suggests that planting of larger suckers could result in lower predation. This recommendation has previously been proposed only to enhance survival of several sport fishes (e.g., Keith and Barkley, 1971; Stein et al., 1981) but not in behalf of an imperiled species. Flathead catfish in the upper Gila River seldom exceed 750 mm and fish that size would consume razorback suckers up to about 130 mm (Fig. 1). Flathead catfish have the capability to swallow considerably large prey, however. We have collected several specimens over 500 mm long from the Gila River that had eaten carp more than half the length of the catfish. We have no data concerning predation by flathead catfish on razorback suckers longer than those reported here. However, flathead catfish longer than 500 mm are uncommon in the upper Gila River, and razorback suckers in the range of 300 mm should be immune to predation except by the largest individuals. ! Stocking in winter has clear advantages over that done in other seasons. Because predation by warmwater fishes should be less intense at colder tem- peratures (e.g., Brown, 1957; Lagler et al., 1977), stocked fish can acclimate to i riverine conditions, find suitable stopping areas (cover), and avoid predation over longer stream distances and for a longer period of time. Presumably, winter- stocked fish would remain about the same size until resumption of growth in