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1 K <br />2 <br />and mice. The abundance, widespread distribution, and omnivorous feeding <br />behavior of this introduced fish may affect populations of rare and endangered <br />fishes in the Green River basin. <br />Native to North America, channel catfish (Ictalurus aunctatus) was <br />formerly restricted to larger streams tributary to the Mississippi River, <br />Great Lakes, and Gulf of Mexico (Jordan and Evermann, 1896) but has been <br />widely introduced elsewhere (Lee et al., 1980). It was stocked in the <br />Colorado River basin as early as 1892 (Allen and Roden, 1978) and introduced <br />into lakes in Utah about 1888; many stockings were subsequently made into the <br />Green and Colorado rivers (Sigler and Miller, 1963). <br />The channel catfish is now common to abundant in rivers of the upper <br />Colorado River basin (Fig. 1), including the Green and Yampa rivers in <br />Colorado and Utah (Holden and Stalnaker, 1975x, 1975b; Tyus et al., 1982). <br />Originally proposed to enhance sportfishing in a faunally depauperate river <br />(Jordan, 1891), fishing for channel catfish in the Green and Yampa rivers is <br />virtually non-existent. However, establishment of the fish in the Colorado <br />River basin has been implicated in decline of rare and endangered native <br />fishes (Holden and Stalnaker, 1975x; Marsh and Brooks, 1989). <br />Little is known about growth or food habits of channel catfish in the <br />Green and Yampa rivers or about its interactions with the native fauna. <br />Although channel catfish are locally abundant, young fish examined at the end <br />of the first growing season are small, and large individuals are rare. This <br />observation suggested that environmental conditions may limit growth and hence <br />attainment of large size in channel catfish. Lynch and Lemons (in litt.) <br />reported slow growth of 23 channel catfish in the Yampa River; however, small <br />