7918

• UCREFRP Catalog Number: 7918
• Author: Scoppettone, G. G., M. Coleman and G. A. Wedemeyer.
• Title: Life History and Status of the Endangered Cui-ui of Pyramid Lake, Nevada.
• USFW Year: 1986.
• USFW - Doc Type: \
• Copyright Material: NO

individually sorted macroinvertebrates, and iden-
tified and counted zooplankton with the aid of a
compound microscope (x 100). Numerical analyses
of zooplankton were made by counting the organ-
isms in a Sedgewick-Rafter cell; three to five counts
from the I-mL cell were made for each fish and
extrapolated for the entire sample volume. The
relative food value of each organism eaten was esti-
mated from the carbon equivalents developed by
Galat and Vucinich (1983) for Pyramid Lake.
Of 17 adult cui-ui collected from the prespawning
aggregation off the delta in 1983, 14 contained
food (Table 5). This observation differs from
those of Johnson (1958) and Koch (1972), who
suggested that adults ceased feeding after they
entered the prespawning aggregation. The fish
collected had fed almost exclusively on two species
of zooplankton-Diaptomus sicilis and Ceriodaph-
nia quadrangula. Lider and Langdon (1978) found
these two species to be the most abundant
zooplankters in Pyramid Lake, ranked in the same
order of abundance as in the cui-ui guts examined.
Although D. sieilis composed only 46% of the total
number of organisms eaten, it contributed 71 % of
the total carbon. Chironomid larvae and algae
occurred in only trace amounts. Other members of
the genus Chasmistes are also believed to be plank-
tivorous (Hubbs and Miller 1953; Moyle 1976; Miller
and Smith 1981). This belief is based on the similar

19

terminal position of the mouth, and the presence
of long filamentous gill rakers.
Most catostomids feed most actively at night
(Moyle 1976), and we suspect that peak feeding
among members of the prespawning aggregation
was at night, since this is when zooplankters are
concentrated near the surface (Lider and Langdon
1978) and when our fish bearing sonic tags were
most active. During most of the day the fish
remained near the mouth of the river, where forag-
ing opportunity was known to be limited.

Larvae and Young of the Year

Food of larvae and postlarvae in the Truckee
River was determined by placing test fish, taken
from the Pyramid Lake Cui-ui Hatchery immediately
after swim-up on 21 April 1981, into a fabricated
backwater habitat that consisted of two shallow
meandering channels dug off a natural braid of the
lower Truckee River, 20 km upstream from Pyramid
Lake. The habitat closely approximated that in back-
waters along the lower Truckee River. Larvae were
introduced 3 weeks after the channels were
constructed. The fish were able to leave by enter-
ing either an upstream or downstream trap. More
than 80 % of the larvae eventually caught were taken
in the downstream trap within 3 days after their
release. As the remaining fish moved out, a small

Table 6. Stomach contents of 42 larval and early juvenile cui-ui (12-28 mm long) from a natural
side channel of the Truckee River, 1981 (T =: trace, less than 0.5%).

Stomach contents

Total
number
(%)

Frequency of
occurrence
(%)

Total
carbon
(%)

Macroinvertebrates
Chironomidae
Larvae
Pupae
Amphipoda
Zooplankton
Copepoda
Cladocera
Ostracoda
Rotifera
Nauplii
Algae
Pollen

26 86 56
I 10 1
1 5 3
20 69 18
32 36 15
3 14 5
1 7 T
10 21 2
T 70 T
7 5 T