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Genus Gila
<br />Chubs of the Genus Gila are found
<br />throughout the southwestern United
<br />States and western Mexico. The tax-
<br />onomic history of this group is long,
<br />clouded and uncertain, as are the current
<br />systematics. Principal cause of these prob-
<br />lems has been lack of knowledge regard-
<br />ing geographic and individual variation
<br />(Rinne 1976). Members of the genus Gila
<br />have either been lumped together into
<br />"ecotypes" of "superspecies" or divided
<br />into a plethora of species and genera. In
<br />terms of species found in the upper Col-
<br />orado River the bonytail, Gila elegans, was
<br />considered variant of the roundtail chub,
<br />Gila robusta, (Ellis 1914), or a subspecies
<br />of the Gila robusta complex (Miller 1946).
<br />Recent investigators (Smith, et al. 1979)
<br />concluded that there are three separate
<br />and identifiable species in the upper Col-
<br />orado River mainstem based on analysis
<br />of 34 morphometric and meristic charac-
<br />teristics. These are the roundtail chub,
<br />Gila robusta, the humpback chub, Gila
<br />cypha, and the bonytail, Gila elegans. All
<br />three are currently found in Colorado. A
<br />fourth member of this genus, the Rio
<br />Grande chub, Gila pandora, is found in the
<br />Rio Grande Basin of Colorado.
<br />Much remains to be learned regarding
<br />exact taxonomic status of this genus. In
<br />the mainstem rivers where natural habi-
<br />tats and flow regimes are disturbed
<br />through construction of impoundments
<br />or water diversions, barriers separating
<br />these three species evidently breakdown
<br />and hybridization has resulted. In Col-
<br />orado, chubs have been collected which
<br />exhibit a complete gradation of physical
<br />characteristics from the humpback to
<br />bonytail to the roundtail chub. Care must
<br />be taken when working with represen-
<br />tatives of this genus, not only must
<br />physical characteristics be examined but
<br />geographic location should be taken into
<br />account.
<br />For additional information regarding
<br />the genus Gila see Wick, E.J., T.A. Lytle,
<br />and C.M. Haynes. 1981. Colorado Squaw-
<br />fish and Humpback Chub Population and
<br />Habitat Monitoring, 1979.1980. Progress
<br />Report, Endangered Wildlife Investiga-
<br />tions. SE-3-3 Col. Div. of Wildlife, Denver
<br />156pp.
<br />
<br />1. a. Caudal peduncle deep, anal rays 8,
<br />limited to Rio Grande Basin.
<br />RIO GRANDE CHUB Gila pandora.
<br />b. Caudal peduncle slender, anal rays
<br />usually more than 8, found in
<br />Colorado River Drainage System.
<br />Go to number 2.
<br />2. a. No nuchal hump, frontals nearly
<br />straight, dorsal and anal rays
<br />usually nine.
<br />ROUNDTAIL CHUB Gila robusta
<br />b. Nuchal hump present in specimens
<br />over 5.9 inches, frontals concave
<br />above eyes in lateral profile, dorsal
<br />rays 9 or 10, anal rays 10 or 11.
<br />Go to number 3.
<br />3. a. Nuchal hump abrupt, dorsal rays
<br />
<br />KEY TO THE GENUS GILA
<br />usually 9, anal rays usually 10, in
<br />young less than 5.9 inches the eye
<br />diameter less than 2/3 caudal pedun-
<br />cle depth, snout overhangs upper
<br />lip.
<br />HUMPBACK CHUB Gila cypha.
<br />b. Nuchal hump not abrupt, dorsal
<br />rays usually 10, anal rays usually 10
<br />or 11, in young less than 5.9 inches
<br />the eye diameter greater than 2/3
<br />caudal peduncle depth, snout not
<br />overhanging upper lip.
<br />BONYTAIL Gila elegans.
<br />Note: Key characteristics for G.
<br />robusta, G. cypha, and G. elegans
<br />taken from Smith, et al. 1979.
<br />
<br />
<br />
<br />Gila chubs from top to bottom: humpback chub, bonytail, and roundtail chub. Photo by
<br />Patricia Shrader, Q.S. Fish & Wildlife Service.
<br />27 Colorado's Little Fish
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