436
JAMES E. DEACON AND W. L. MINCKLEY
Minckley, 1970). These fishes have been variously interpreted, over the
years, as ecological types of one species or as different genera, but have
recently been defined as full species (Rinne, 1969; Holden and Stalnaker,
1970). Gila cypha still is in doubt (Holden and Stalnaker, 1970), principally because of collection of numbers of putative hybrids between it and
other species from a disturbed part of the river basin (the Lake Powell
area). Gila cypha is rare in collections, and its ecology may only be
inferred.
Vanicek et al. (1970) found G. elegans and the less streamlined G.
robusta living sympatrically in pools and eddies of the Green River, Utah,
sometimes adjacent to, but never in, swift currents. Swift-water forms of
the bluehead mountain-sucker {Pantosteus discobolus), a species with
morphotypes differentiated similar to those of G. elegans and G. robusta
(in the mainstream and in smaller tributaries, respectively), were consistently in current, and usually in the swiftest parts. The highly variable
Rhinichthys osculus also has numerous morphotypes that similarly reflect
the impact of current on its body form within the Colorado River system.
The extreme body shape of the bony tail chub (G. elegans) perhaps
correlates most closely with their potential for movement through swift
waters in periods of low or modal flow, and within current in times of flood.
The general lack of development of organs of attachment in Colorado
River fishes must reflect the instability of bottoms and channels in that
remarkably erosive stream. Instead, a highly modified body shape permits
the fish to be held against the bottom under conditions of turbulence
(through pressure of water on the curved dorsal surfaces and expanded
fins). Shape thus substitutes for holdfast organs. It is notable that
bonytail chub maintaining reproducing populations in larger impoundments of the Colorado system retain their streamlined body shapes, apparently moving about in an active, limnetic manner (Minckley, 1971)
as do some oceanic fishes of similar morphology.
Basic modifications of body shape seem to have occurred in parallel in
many groups of fishes, and these modifications may relate to sediment loads
and to river currents which carry them. The woundfin (Plagopterus argentissimus) is a species characteristic of the mainstream of the relatively swift
and silt-laden Virgin River, Utah-Arizona-Nevada (Deacon et al, 1971).
Many of its traits are similar to features of some bottom-dwelling, swiftwater, silty-stream minnows of eastern United States, and elsewhere.
Barbels are present on the eastern fishes now referred to the genus
Hybopsis (Moore, 1968) and also are well developed on Plagopterus.
Dermal keels similar to those of the woundfin are present on the anterodorsal scales of Hybopsis gelida (Cross, 1967). Coarse, close-set papillae
on the intermandibular (gular) region of the woundfin (Snyder, 1915) are
JAMES E. DEACON AND W. L. MINCKLEY
Minckley, 1970). These fishes have been variously interpreted, over the
years, as ecological types of one species or as different genera, but have
recently been defined as full species (Rinne, 1969; Holden and Stalnaker,
1970). Gila cypha still is in doubt (Holden and Stalnaker, 1970), principally because of collection of numbers of putative hybrids between it and
other species from a disturbed part of the river basin (the Lake Powell
area). Gila cypha is rare in collections, and its ecology may only be
inferred.
Vanicek et al. (1970) found G. elegans and the less streamlined G.
robusta living sympatrically in pools and eddies of the Green River, Utah,
sometimes adjacent to, but never in, swift currents. Swift-water forms of
the bluehead mountain-sucker {Pantosteus discobolus), a species with
morphotypes differentiated similar to those of G. elegans and G. robusta
(in the mainstream and in smaller tributaries, respectively), were consistently in current, and usually in the swiftest parts. The highly variable
Rhinichthys osculus also has numerous morphotypes that similarly reflect
the impact of current on its body form within the Colorado River system.
The extreme body shape of the bony tail chub (G. elegans) perhaps
correlates most closely with their potential for movement through swift
waters in periods of low or modal flow, and within current in times of flood.
The general lack of development of organs of attachment in Colorado
River fishes must reflect the instability of bottoms and channels in that
remarkably erosive stream. Instead, a highly modified body shape permits
the fish to be held against the bottom under conditions of turbulence
(through pressure of water on the curved dorsal surfaces and expanded
fins). Shape thus substitutes for holdfast organs. It is notable that
bonytail chub maintaining reproducing populations in larger impoundments of the Colorado system retain their streamlined body shapes, apparently moving about in an active, limnetic manner (Minckley, 1971)
as do some oceanic fishes of similar morphology.
Basic modifications of body shape seem to have occurred in parallel in
many groups of fishes, and these modifications may relate to sediment loads
and to river currents which carry them. The woundfin (Plagopterus argentissimus) is a species characteristic of the mainstream of the relatively swift
and silt-laden Virgin River, Utah-Arizona-Nevada (Deacon et al, 1971).
Many of its traits are similar to features of some bottom-dwelling, swiftwater, silty-stream minnows of eastern United States, and elsewhere.
Barbels are present on the eastern fishes now referred to the genus
Hybopsis (Moore, 1968) and also are well developed on Plagopterus.
Dermal keels similar to those of the woundfin are present on the anterodorsal scales of Hybopsis gelida (Cross, 1967). Coarse, close-set papillae
on the intermandibular (gular) region of the woundfin (Snyder, 1915) are