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dsmundson (1986) studied the use of'ponds along the Colorado River for their potential for rearing hatchery-produced Colorado squawfish. He reported that largemouth bass predation by fish over 100 mm TL significantly reduced the survival of stocked squawfish. In fact, squawfish were selected over fathead minnows (Pimephales promelas), red shiners (No is lutrensis), and young-of- the-year green sunfish. However, in the laboratory, captive bass preyed equally on fathead minnows and Colorado squawfish. The preference for soft- rayed forage fish (e.g., minnows) over spiny-rayed fish (e.g., sunfish) by ' largemouth bass has been documented (Holton 1977). Usmundson (1986) reported that small squawfish were consumed more readily than larger ones. This is probably related to the relation between the size of the bass's mouth and the depth of the prey as described by Lawrence (1957). Immediately after stocking Colorado squawfish in riverside ponds along the Upper Colorado River, largemouth bass completely switched their diets to squawfish that was related to prey abundance and vulnerability since the squawfish were in a strange lenvironment and were probably stressed from handling prior to stocking. A further threat exists from bass that escape downstream into the riverine I, habitat. Part of the recovery program involves habitat development and maintenance such as building jetties to form quiet eddies as-holding areas and backwaters as nursery areas (U.S. Fish and Wildlife Service 1986). The rapid growth of Colorado squawfish described by Usmundson (1986) provides an 1 `excellent method for obtaining rapid growth on natural food that should be accompanied by better survival of the stocked squawfish during the critical ,early years of life. However, warmwater predatory sport fish are adapted for ,and probably will seek the habitat created by madmade backwaters. In fact, ;largemouth bass are not numerous in the riverine habitat of the Colorado River !but occupy the quiet backwater areas and could pose severe problems to 'recovery of the rare Colorado River fishes-in such areas (Miller et al. 1982; ;Tyus, Mc Ada and Burdick 1982; Valdez h't al. 1982). BI uegi 11 Habitat Bluegills are most abundant in ponds, lakes, and sluggish streams usually with -abundant vegetation or other cover such as tree roots and limbs (Carlander 1977). In streams of the Sierra Nevada foothills, California, abundance of bluegills was positively correlated with depth of stream, % rooted vegetation, % pools, and number of fish species (Moyle and Nikols 1973). Bluegills.are rare or incidental throughout the Upper Colorado River except in Lake Powell on the mainstem and Navajo Reservoir on the San Juan River (Tyus et al. 1982). They are abundant in the littoral zone of both reservoirs where the habitat is particularly suited to their ecological requirements. Food Habits Young bluegills feed on microcrustaceans, zooplankton, and aquatic insects; adult bluegills feed mainly on aquatic insects, small crayfish, and small fish (Carlander 1977). Optimum temperature for feeding was 27 C with a maximum of 31 C (Kitchell et al. 1974). In another study, bluegills preferred temperatures of 28-33 C in the field and essentially the same in the laboratory (Neill and Magnuson 1974). 7