7621

• UCREFRP Catalog Number: 7621
• Author: Woodling, J.
• Title: Colorado's Little Fish
• USFW Year: 1985.
• USFW - Doc Type: A Guide to the Minnows and Other Lesser Known Fishes in the State of Colorado.
• Copyright Material: NO

Family Cypnnidae Genus Gila
BONYTAI L
Gila elegans
(Baird and Girard)
A highly streamlined fish; concave skull
arching into a nuchal hump predorsally;
caudal peduncle pencil-like, long and
slender; snout does not overhang upper
lip; scales often minute or absent from
chest, stomach and caudal peduncle; fins
falcate with 10 dorsal fin rays, and 10-11
anal fin rays; in young, less than 5.9
inches, eye diameter greater than 2/3
caudal peduncle depth.
Adults are dark on top, light below.
Often they are very dark in clear waters
and pale in turbid waters. Fins are dusky
with yellow pigment near base (Minckley
1973). Adults (7 years of age) can be 14
inches long and weigh more than one
pound (Vanicek and Kramer 1969).
Range: Found historically throughout
the Colorado River Drainage, in recent
years bonytail have only been taken from
the Green River in Utah and lakes Havasu
and Mohave (Miller, et al. 1982). Jordan
(1891) reported one bonytail from the
Gunnison River near Delta and other
specimens have been taken in the Green
River in Colorado. No bonytails had been
collected in Colorado for several years
until 1984, when one individual was
collected at the Black Rock area of the
Colorado River west of Grand Junction,
Colorado, (L. Keading, personal com-
munication). The bonytail is listed as a
federal and state endangered species.
Habitat: Little is known about this
species. The bonytail prefers eddies and
pools, not swift current (Vanicek and
Kramer 1969).
The two factors thought to be tied to the
decline of the bonytail are lower water
temperatures (attributable to reservoir
construction) and hybridization. After
a reservoir is constructed, the water
released from the impoundment is often
taken from the deeper layers of the lake.
These waters are much colder than the
surface water and lower river temperatures
downstream of reservoirs. Hamman
(1982b) found that 96% of all bonytail
eggs incubated in cold water (54-56°F)
failed to hatch while optimal hatching and
larval survival took place in warmer water
(68-70°F). Juvenile bonytail, 3-5 inches,
exhibited the greatest stamina in sus-
57
..
r
Bonytail. Photo by Patricia Shrader. U.S. Fish & Wildlife Service.
r-------7--T ? I
r IJ -I o
r
I

-- --- '
? 7"1
I I ' !
II i
` 1
I I i IiI I ,r1 -
j_- ----- --'
Distribution by County of the bonytail.
tained swimming tests in 80°F water and
least stamina in 580F water (Bulkley, et
al. 1982). Lower water temperatures down-
stream of many impoundments could
negatively impact bonytail.
Several studies (Miller, et al. 1982 and
Minckley 1973), note that investigation of
T ,
I
1 -
' -I
I ?
I I
F-----
I I -
--j --rte I
I Po
I -T- -?

the genus Gila are hindered by the large
number of hybrids that are found when
two chub species of this genus are found
together. As hybridization becomes more
extensive in an area, the numbers of
genetically "pure" individuals decrease,
diluting the gene pool.
Colorado's Little Fish 30