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<br />98
<br />Humpback chub, GilacyphaMiller
<br />(Fig. 49; Map 13)
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<br />Gilo cypho, Miller, 1946c: 410/ 1965: 130/ 1963c: 9/ 1964a: 9/ 19646
<br />26/ 1968: 2/ 1969: n.p./ 1972a: 242. Wallis, 1951: 87. Lowe, 1960:
<br />171. Sigler and Miller, 1963: 163. Miller and Lowe, 1964: 133/ 1967: 138.
<br />Anonymous, 1966: F-19. Bradley and Deacon, 1967: 230. Cole, 1968: 471.
<br />Moore, 1968: bl. Holder and Stahlnaker, 1970: 409. Rinne and Minck.ley, 1970:
<br />18. Minckley, 1971: 185. ~
<br />Body streamlined; skull concave on dorsum. Nape abruptly produced at occiput
<br />into a truncate, prominant hump, which often projects forward to overhang occiput
<br />in large adults. Caudal peduncle thin, somewhat pencil-like but not greatly elon-
<br />gated, its length divided by length of head less than 1.0; head length divided by
<br />caudal peduncle less than 5.0. Squamation often incomplete, or scales embedded
<br />deeply (especially on hump). Fins large, falcate. Origin of dorsal fin about equi-
<br />distant between snout and caudal-fin base. Dorsal fin-rays usually 9, and anal i
<br />r fin rays 10 or more. Mouth inferior, overhung by snout. Pharyngeal arch small,
<br />its lower ramus short, teeth usually 2, 5-4, 2.
<br />Coloration as in G. elegans, but rarely with chromatophore pigmentation at
<br />bases of fins.
<br />This species is in some respects even more highly specialized than
<br />Gila elegans for life in the turbulent Colorado River. It once occurred down-
<br />. stream to just below the present site of Hoover Dam (on the basis of skeletal ,
<br />material from an Indian site at the now-inundated Catdaw Cave flooded
<br />by Lake Mohave; Miller, 1955), and upstream in the larger portions of the
<br />main river, and in the Green River of Utah (Sigler & Miller, 1963; Miller,
<br />1963c, 19646). At present, it seems restricted to the Grand Canyon and
<br />above, and is known from only a few, scattered and sporadic collections. `
<br />~As noted above, the humpback chub is involved in mass hybridization with
<br />other Gila in the area of Lake Powell, as alluded to by Holden &Stahlnaker
<br />(1970), who wisely retained it as a full species.
<br />Unique features of this species, not at all overly-emphasized in the
<br />illustration, center about the extremely-produced hump on its anterodorsal
<br />surface. Also, the belly and lower part of the head are flattened, the ',
<br />mouth is essentially horizontal, and overhung by a produced, fleshy snout.
<br />It would seem that the hump acts as a barrier to passing water, forcing the p
<br />~ fish's body against the bottom. Perhaps the pronounced grooves laterally
<br />
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