7184

• UCREFRP Catalog Number: 7184
• Author: Minckley, W. L. and E. S. Gustafson
• Title: Early Development of the Razorback Sucker,
• USFW Year: 1982
• Copyright Material: YES

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EARLY DEVELOPMENT OF THE RAZORBACK SUCKER,
XYRA UCHEN TEXANUS (ABBOTT)
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W. L. Minckley' and Eric S. Gustafson'
ABsT ACT.- Fertilized ova of razorback sucker, Xyrauchen texanus, were adhesive for 3 to 4 hours after fertiliza-
tion. Cleavage was completed at 24 hours, gastrulation occurred at 34 hours, and blood circulation was established at
117 hours. Hatching occurred from 5.2 to 5.5 days after fertilization. Larvae were from 6.8 to 7.3 mm TL at hatch-
ing. Yolk was assimilated at 13 days (10 mm TL). All fins were formed and had ossified rays at 64 days (27 mm TL).
The unique nuchal keel appeared about 200 days after fertilization.
The razorback sucker, Xyrauchen texanus
(Abbott), is endemic to the Colorado River
basin. As with much of the southwestern ich-
thyofauna (Pfister 1981), it is declining in
abundance (Minckley 1983). A program was
commenced in 1974 to develop means of
propagating the species (Toney 1974) and to
delineate certain aspects of its life history.
We studied embryological, larval, and juve-
nile development of the species in 1974-75.
Although our data are somewhat outdated in
light of recent studies of catostomid larvae
(reviewed by Fuiman and Witman 1979), al-
most nothing has appeared on the early life
history of this unique species. Winn and
Miller (1954) presented a key to postlarval
-fishes of the lower Colorado River basin that
"included photographs and some descriptions
of young X. texanus. A photograph by
Douglas (1952: Fig. 3) was reidentified by
Winn and Miller as speckled dace (Rhi-
nichthys osculus [Girard]) rather than X. tex-
nus. The present paper thus describes and
gures early life-history stages of the razor-
?boratory-reared k sucker as determined from hatchery-and
11 individuals.
METHODS
Initial information on hatchery propaga-
on and rearing of razorback suckers origi-
nated from adult fish seined near Cotton-
wood Cove in Lake Mohave, Arizona
'Nevada, in winter 1974, and was compiled
'Department of Zoology, Arizona State University, Tempe, Arizona 85287.
by personnel at Willow Beach National Fish
Hatchery (in part, Toney 1974). Eggs were
stripped from females and fertilized, and de-
veloping young were initially housed in an
indoor raceway at a mean water temperature
of 14 C, then transferred 13 days post-
hatching to an outdoor raceway where water
temperature averaged 15 C. Samples were
preserved daily in 10 percent formalin during
the first month, and intermittently thereafter.
Late postlarval and juvenile phases described
below are based on the 1974 cohort.
Additional adults were trammel netted
from below Hoover Dam and in the vicinity
of Carp Cove in Lake Mohave in March-
April 1975. Most males were in active
spawning condition, but females were either
spent or not yet mature. Suitable females
were interperitonealy injected with human
chorionic gonadotropin, which induced
oocyte maturation. A few hours after in-
jection about 5,000 eggs were stripped from
a single female and immediately fertilized
with sperm of two males, as has been ob-
served in nature (Douglas 1952). It is notable
that water-hardened eggs obtained from
naturally-matured females in 1974 were 2.9
mm diameter, but comparable ova obtained
from hormone-induced maturation were 1.8
mm diameter. This disparity is far greater
than has before been recorded in catostomid
ova diameters (Fuiman and Trojnar 1980).
We assume it resulted from precipitous mat-
uration after hormone injection, but have no
553
1101- 6"J LAStU i NAIL/DIes71 41 - Sn. So.