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<br />1 <br />I ABSTRACT <br /> Colorado squawfish (Pt ychocheilus lucius) of the upper <br /> Colorado River are thought to experience a high rate of <br /> mortality during the first few years of life. Occurrence <br /> of the nonnative largemouth bass (Micropterus salmoides) in <br /> <br /> Colorado River backwaters, a preferred habitat of young-of- <br />the-year and juvenile squawfish, may be an important factor <br />affecting squawfish survival. Largemouth bass food habits <br />were studied in riverside ponds and in the laboratory to <br />determine squawfish vulnerability to bass predation. Also, <br />the potential usefulness of riverside ponds for squawfish <br /> culture was investigated. <br /> Hatchery-reared Colorado squawfish (45-145 mm long) <br /> were stocked at 3,090 fish/ha in five gravel-pit ponds <br /> (0.85-3.16 ha) adjacent to the Colorado River in the fall <br /> of 1983 and 1984, and in the summer of 1984. Resident <br /> largemouth bass and several species of forage fish varied <br /> in relative abundance among ponds. Growth and survival of <br /> stocked squawfish were monitored as were bass stomach con- <br /> tents before and after squawfish stocking. Three labora- <br /> tory experiments were conducted to determine the preference <br /> of largemouth bass when offered Colorado squawfish and one <br /> f <br /> o <br />three alternative prey types: (1) fathead minnows (Pime- <br /> hales promelas), (2) red shiners (Notropis lutrensis), and <br /> (3) green sunfish (Lepomis cyanellus). Another laboratory <br /> experiment tested the prey-size preference of largemouth <br /> <br /> X111