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57 features. This systematic and taxonomic dilemma represents a frustrating problem to the CRFP field studies particularly since the fish are uncommon to rare (prevents sacrifice of sufficient numbers for appropriate taxonomic studies) and since an identification must be made eventually to document species distribution and habitat requirements. The more abundant and nonendangered G. robusta appears to be a distinct species in nearly all reaches of the Upper-Colorado River (Figure 2), except where it occurs sympatrically with G. cypha. Although G. robusta rarely exceeds 300 mm total length (TL), one individual of 486-;mTL was captured in the upper reaches. This species usually exhibits a terminal mouth, scaled back, robust caudal peduncle, no nuchal hump, and generally 9 dorsal and 9 anal fin rays. Coloration varies but usually the belly is white, the sides silver- gray, and the back, green. This coloration is accented by an orange belly during spawning in June and July. The rare ~ cypha is also usually distinct (Figure 3). Individuals rarely exceed 370 rom TL, but maximum size was 392 rom Tt. The species exhibits an abrupt, scaleless nuchal hump, flattened head, overhanging fleshy snout, subterminal mouth, small eye, relatively long fins, and usually 9 dorsal and 10 anal fin rays. Coloration is fairly consistent; creamy white belly and sides, with tints of yellow and green on the sides, and a dull green-silver back. Spawning individuals in early JUne have light orange bellies. Gila elegans was not found in the Upper Colorado River during this study either as pure strains, suspected variants, or integrades. The species in characterized by a terminal mouth, a slender body, pencil-thin caudal peduncle, the absence of a nuchal hump, and usually 10 dorsal and 10 anal fin rays (Figure 4). The color is silver-gray and darker dorsally. Field identification is sometimes difficult for adult Gila that exhibit features intermediate between ~ cypha and ~ robusta, e.g. a moderate, partially scaled nuchal hump; a slightly inferior mouth; varied coloration and fin ray counts. This problem is intensified when identifying young-of-the- year and juveniles. Thus, several methodologies are being employed by CRFP to aid identifica- tion afield: 1. examination of general morphology 2. enumeration of dorsal and anal fin rays 3. measurement of nuchal depth 4. intensive taxonomic analyses General Morphology Since detailed anatomic and meristic measurements are impossible to secure afield from live fish, examination of general and relative anatomic features becomes a vital criterion for identification at capture or at a later date when compared with data of other fishes. Morphology of ~ cypha and ~ robusta, as described earlier, was examined closely to assess the similarity of individuals with the described holotype (Miller 1946).