7109 ‎(2)‎

• UCREFRP Catalog Number: 7109
• Author: Marsh, P. C.
• Title: Digestive Tract Contents of Adult Razorback Suckers in Lake Mohave, Arizona-Nevada
• USFW Year: 1987
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

118
NOTES
TABLE 1.-Contents of digestive tracts of preserved
adult razorback suckers from Lake Mohave, Arizona-
Nevada. Frequency of occurrence is percentage of tracts
containing a particular item among a sample of 32 fish
collected in 1980 and 1984. Predominance is percentage
of tracts in which an item contributed the greatest pro-
portion to total contents. Number is mean number of
identifiable animals per milliliter of undiluted digestive
tract contents among 24 specimens collected in 1984.
Fre-
quency
of
occur- Predomi-
rence nance Number
Item (°Io) (%) (SD)
Cladocera
Bosmina sp. 100 53 284 (314)
Daphnia sp. 72 3 58 (65)
Chydorus sp. 16 0 3 (2)
Leptodorus sp. 9 0 2 (0)
Rotifeta 53 0 42 (48)
Ostracoda 53 0 12 (11)
Copepoda 34 0 6 (5)
Insecta
Chironomidae 3 0 3 (2)
Diatoms 88 6
Filamentous algae 44 12
Detritus 56 25
Inorganics (e.g., sand) 16 0
Discussion
Hubbs and Miller (1953) described the long,
fine gill rakers of razorback suckers, noted their
similarity to those of lake-dwelling, presumably
planktivorous, suckers of the genus Chasmistes,
and found microplankton between rakers and
pharyngeal pads of preserved razorback suckers.
Razorback suckers have been reported to feed on
planktonic crustaceans in May in Lake Mohave
(Minckley 1973) and on zooplankton swarming
near artificial light in Lakes Mead and Mohave
(Allan and Roden 1978). Dill (1944) examined
digestive tracts of four specimens collected in 1942
from the Colorado River near Parker, Arizona;
they were packed with silt rich in diatoms and
filamentous algae. Banks (1964) found algae and
plant debris and larval ephemeropterans, trichop-
terans, and dipterans in digestive tracts of razor-
back suckers from the Green River, Colorado-
Utah. Eight razorback suckers from the same
stream had tracts containing mud or clay and in-
cluding chironomid larvae and plant stems or
leaves (Vanicek 1967).
Planktivory with a definite component of ben-
thic feeding is indicated among fish examined here.
Zooplankton may be captured anywhere in the
water column, yet truly planktonic forms as Bos-
fnina sp. and Daphnia sp. also could be derived
from the sediment-water interface where they ac-
cumulate after death. Observers of feeding by ra-
zorback suckers have noted "bouncing" up and
down during forward movement near the bottom
(Minckley 1973). The fish also excavates softer
substrates, actively taking large volumes of sedi-
ment into the mouth, manipulating the sediment,
and passing material out through the opercules
while presumably retaining foodstuffs. Razorback
suckers sometimes burrow headfirst to depths of
10 cm or more (to eye level) and perform this
activity for several minutes either at a particular
place or with forward movement over distances
approaching a meter (original observations at
Dexter National Fish Hatchery, New Mexico).
In conclusion, although gill raker morphology
and diet were such that feeding obviously included
active planktivory, digestive tract contents in adult
razorback suckers from Lake Mohave included
benthic material. It is not clear if the latter was
selected as food or was a byproduct of the fish's
burrowing or sediment-excavating activities.
Acknowledgments
Funding was from the U.S. Fish and Wildlife
Service, Endangered Species Office, Albuquerque,
New Mexico (Contract 14-16-0002-81-223) to
Arizona State University. Collection permits were
granted by the Arizona Game and Fish Depart-
ment and the Nevada Department of Wildlife. W.
L. Minckley, J. N. Rinne, and two anonymous
individuals reviewed the manuscript.
References
Allan, R. C., and D. L. Roden. 1978. Fish of Lake
Mead and Lake Mohave. Nevada Department of
Wildlife, Biological Bulletin 7, Reno.
Banks, 7. L. 1964. Fish species distribution in Dino-
saur National Monument during 1961-1962. Mas-
ter'sthesis. Colorado State University, Fort Collins.
Bozek, M. A., L. J. Paulson, and J. E. Deacon. 1984.
Factors affecting reproductive success of bonytail
chubs and razorback suckers in Lake Mohave. Final
Report, Contract 14-16-0002-81-251, to U.S. Fish
and Wildlife Service, Albuquerque, New Mexico.
Dill, W. A. 1944. The fishery of the lower Colorado
River. California Fish and Game 30:109-211.
Hubbs, C. L., and R_ R. Miller. 1953. Hybridization
in nature between the fish genera Catostomus and
Xyrauchen. Papers of the Michigan Academy of Sci-
ence, Arts and Letters 38:207-233.
McAda, C. W., and R. S. Wydoski. 1980. Razorback
sucker, Xyrauchen texanus, in the upper Colorado
y