VII. DESERT FISHES
437
superficially quite like those on H. gelida (Branson, 1966). General
shape of Plagopterus (depressed, ventrally flattened head, dorso-lateral and
relatively small eyes; large fins; etc.) all strongly resemble the shapes of
a number of riverine Hybopsis, and even of diverse other fishes: river
sturgeons of the genus Scaphirhynchus (Bailey and Cross, 1954); diverse
catfishes (Hora, 1930) and cyprinids (Nikolsky, 1961) of Eurasia and
elsewhere; loaches (Cobitidae; Hutchinson, 1939); North American catfishes (Taylor, 1969); and other groups of similar habit and habitat from
other parts of the world.
Barbels of those silty-water fishes that have been studied, and in general
of fishes from any dimly lit environment, are profusely invested with
chemoreceptors, the numbers and sizes of which often increase with growth
of the fish (Davis and Miller, 1967). Similar organs may also be distributed over the lower surface of the head and body, lips, and sometimes
even on the interradial membranes of fins. These organs greatly increase the surface area that may provide information on the immediate
environment.
Two forms of the minnow Hybopsis aestivalis from turbid streams of
the southern Great Plains swim slowly just above the bottom with their
pectoral fins spread widely and barbels in contact with the sand (Davis
and Miller, 1967). There was no evidence of visual selection of food by
these fishes, despite artificially clear water in aquaria, but they quickly
detected dried and live foods that sank to the bottom, searching with exaggerated movements and even greater spreading of the fins. No change
toward sight feeding was evident after three months in clear-water aquaria.
The woundfin has almost identical behavior in captivity, but it will occasionally rise to take floating objects or live foods at a considerable distance
from the bottom, or at the surface.
Internal morphological features also correlate with habitats and habits
of fishes. Relative sizes and degrees of development of the brain seem to
reflect with some accuracy the expanded sensory equipment of some other
parts of the body (Miller and Evans, 1965). Fishes with hypertrophy of
the facial lobes of the brain usually have reduced optic lobes, reflecting
less sensory input from vision and more from organs arranged in the skin.
Those fishes that sort food from debris taken into the mouth have vast
numbers of bucco-pharyngeal receptors and correspondingly enlarged
vagal portions of the brain. Skin tasters and mouth tasters obviously predominate in silty waters, and included with the former is the razorback
sucker (Xyrauchen texanus) endemic to the Colorado River (Miller and
Evans, 1965).
As discussed before, fishes of the mainstream of the Colorado River
demonstrate an unusual parallelism in morphology, and this includes not
437
superficially quite like those on H. gelida (Branson, 1966). General
shape of Plagopterus (depressed, ventrally flattened head, dorso-lateral and
relatively small eyes; large fins; etc.) all strongly resemble the shapes of
a number of riverine Hybopsis, and even of diverse other fishes: river
sturgeons of the genus Scaphirhynchus (Bailey and Cross, 1954); diverse
catfishes (Hora, 1930) and cyprinids (Nikolsky, 1961) of Eurasia and
elsewhere; loaches (Cobitidae; Hutchinson, 1939); North American catfishes (Taylor, 1969); and other groups of similar habit and habitat from
other parts of the world.
Barbels of those silty-water fishes that have been studied, and in general
of fishes from any dimly lit environment, are profusely invested with
chemoreceptors, the numbers and sizes of which often increase with growth
of the fish (Davis and Miller, 1967). Similar organs may also be distributed over the lower surface of the head and body, lips, and sometimes
even on the interradial membranes of fins. These organs greatly increase the surface area that may provide information on the immediate
environment.
Two forms of the minnow Hybopsis aestivalis from turbid streams of
the southern Great Plains swim slowly just above the bottom with their
pectoral fins spread widely and barbels in contact with the sand (Davis
and Miller, 1967). There was no evidence of visual selection of food by
these fishes, despite artificially clear water in aquaria, but they quickly
detected dried and live foods that sank to the bottom, searching with exaggerated movements and even greater spreading of the fins. No change
toward sight feeding was evident after three months in clear-water aquaria.
The woundfin has almost identical behavior in captivity, but it will occasionally rise to take floating objects or live foods at a considerable distance
from the bottom, or at the surface.
Internal morphological features also correlate with habitats and habits
of fishes. Relative sizes and degrees of development of the brain seem to
reflect with some accuracy the expanded sensory equipment of some other
parts of the body (Miller and Evans, 1965). Fishes with hypertrophy of
the facial lobes of the brain usually have reduced optic lobes, reflecting
less sensory input from vision and more from organs arranged in the skin.
Those fishes that sort food from debris taken into the mouth have vast
numbers of bucco-pharyngeal receptors and correspondingly enlarged
vagal portions of the brain. Skin tasters and mouth tasters obviously predominate in silty waters, and included with the former is the razorback
sucker (Xyrauchen texanus) endemic to the Colorado River (Miller and
Evans, 1965).
As discussed before, fishes of the mainstream of the Colorado River
demonstrate an unusual parallelism in morphology, and this includes not