7123 ‎(2)‎

• UCREFRP Catalog Number: 7123
• Author: Klima, E. F.
• Title: Voltage and pulse rates for inducing electrotaxis in twelve coastal pelagic and bottom fishes
• USFW Year: 1972
• USFW - Doc Type: Journal of the Fisheries Research Board of Canada
• Copyright Material: YES

THE SOUTHWESTERN NATURALIST 30(1):129-140 MARCH 27, 1985
EFFECT OF INCUBATION TEMPERATURE ON
SURVIVAL OF EMBRYOS OF
NATIVE COLORADO RIVER FISHES
PAUL C. MARSH
ABSTRACT.-Razorback sucker (Xyrauchen texanus [Abbott]), bonytail (Gila elegans Baird and
Girard) and humpback (G. cypha Miller) chubs, and Colorado squawfish (Ptychocheilus lucius)
Girard) comprise the endemic "big river" fish fauna of the Colorado River, western North Amer-
ica. All are near extirpation in the wild. Effects of incubation temperature upon embryo hatch
success were experimentally examined to evaluate potential impacts of cold hypolimnetic reservoir
releases upon species reproductive success. Eggs were spawned and fertilized at 18°C, and embryos
incubated at 5, 10, 15, 20, 25, and 301C. Total mortality of embryos of all species occurred in 12.96
hours at 5, 10, and 30°C; and in 48-60 hours at 15°C for P. Lucius only. Survival and percentage
hatch were highest at 15 and 20°C (G. elegans) or 20°C (all others). Hatched prolarvae were 0.2-1.3
mm TL longer at 20°C than at 15 or 251C. Spinal or other anomalies were more frequent at 15
and 251C than at 20°C. Development rates (V) were similar for all species, 4.4-61 (15°C), 8.4-9.9
(20°C), and 12.4-18.8 (25°C). Because of lower survival and higher incidence of anomalies at 15
and 25°C, optimal temperatures for development and hatching are probably near 20°C. Reproduc-
tion may thus be limited in the wild by low water temperatures, although successful hatching is
certainly riot precluded. Other hypotheses to explain the demise of these fishes in thermally suita-
ble portions of the Colorado River, such as predation upon young, should be examined.
Razorback sucker (Xyrauahen texanus [Abbott]), bonytail (Gila elegans
Baird and Girard) and humpback (G. cypha Miller) chubs, and Colorado
squawfish (Ptychocheilus luci.us Girard) comprise the unique, endemic "big
river" fish fauna of the Colorado River of western North America. All are in
danger of extinction and are listed as threatened or endangered by one or
more of six western states (Deacon et al., 1979), and all but razorback sucker
are considered endangered by the U.S. Fish and Wildlife Service (USDI,
1980).
Historic ranges included larger rivers throughout the Colorado River
basin (razorback sucker, bonytail chub, Colorado squawfish) or middle and
upper Colorado and Green Rivers (humpback chub). Present distributions
are severely limited. Razorback suckers are found only above Grand Canyon
and in lakes Mead, Mohave, and Havasu on the lower Colorado River (Fig.
1); bonytail chub currently persist in Green River and Lake Mohave; hump-
back chub populations persist in the mouth of the Little Colorado River
and in Desolation Canyon of the Green River; and Colorado squawfish are
restricted to the upper river in Colorado, Utah, and Wyoming (Lee et al.,
1980).
Declines of these and other native southwestern fishes have been attributed
to dewatering; mainstream dams and impoundments; altered stream flow,
channel morphology, and water quality; and introduction of exotic fishes
(Miller, 1961; Minckley and Deacon, 1968; Seethaler, 1978; Johnson and
Rinne, 1982). In particular it has been suggested that lowered water temper-
atures associated with hypolimnetic reservoir releases may curtail reproduc-
tion (Vanicek, 1967; Vanicek et al., 1970; Holden, 1973; Seethaler et al., 1976;
Joseph et al., 1977; Kaeding and Zimmerman, 1983).