7229

• UCREFRP Catalog Number: 7229
• Author: Kaeding, L. R. and M. A. Zimmerman
• Title: Life History and Ecology of the Humpback Chub in the Little Colorado and Colorado Rivers of the Grand Canyon
• USFW Year: 1983
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

586
KAEDING AND ZIMMERMAN
nomidae and Simuliidae (Table 2). Two fish
from the Little Colorado contained fish re-
mains, including a fathead minnow Pimephales
promelas about 50 mm long. Although the am-
phipod Gammarus sp. was abundant in many
littoral areas of the Colorado, it was relatively
uncommon among the stomach contents.
Twelve of the 26 humpback chub stomachs from
the Little Colorado and 5 of the 18 stomachs
- from the Colorado were empty. A few fish were
kept in holding pens 1-2 hours before they were
killed; digestion or regurgitation while fish were
in pens or trammel nets may in part account for
the numbers of empty stomachs found. The
large number of organisms in humpback chub
stomachs from the Colorado suggests that food
organisms might be more available in the Col-
orado than in the Little Colorado.
Pathogens
Thirteen species of bacteria, six protozoans,
and the fungus Saprolegnia-all common fish
pathogens-were identified in low incidence
from humpback chubs (Rex Flagg, Fish Disease
Control Center, USFWS, Fort Morgan, Colo-
rado, personal communication). However, many
adult humpback chubs collected from the con-
fluenceand from the lower Little Colorado dur-
ingthe 1981 spawning season showed acute signs
of systemic Aeromonas hydrophala infection, in-
cluding abundant petechia and poor physical
condition.
Lernaea cyprinacea (Copepoda) was the most
conspicuous metazoan parasite encountered.
Infection incidence was highest in winter and
lowest in spring in the Little Colorado and the
confluence (C 4). Only six infected fish were
collected from the Colorado (Table 3). The in-
tensity of L. cyprinacea infection was below that
reported where appreciable mortality of other
host species has occurred (for example, Bauer
1959), but high infection incidence in small
humpback chubs in the Little Colorado during
December could result in mortality from sec-
ondary infection by other pathogens. Optimal
temperatures for the development of L. cypri-
nacea are between 23 and 30 C; the life cycle
cannot be completed below 14 C (Bauer 1959),
near the maximum temperature found in the
Colorado (Fig. 2). Thus, the capture of infected
humpback chubs from the Colorado strongly
suggests movement of the fish from the Little
Colorado.
TABLE 3.-Seasonal incidence of Lernaea cyprinacea
infection of humpback chubs of three length categories
from the Little Colorado River, the confluence, and the
Colorado River. Data are given as number of fish ez-
arained~number infected (percent infected in parenthe-
ses).
Little
Length class Colorado Confluence Colorado
Winter (Dec)
<100 mm 20/9 (45)
100-200 mm 7/5 (71)
>200 mm 50/25 (50)
Total 77/39 (51)
Spring (Feb-May)
<100 mm 50/4 (8) 11/1 (9) 34/0 (0)
100-200 mm 16/1 (6) 12/0 (0) 10/1 (10)
>200 mm 178/8 (4) 48/3 (6) 22/1 (5)
Total 244/13 (5) 71/4 (6) 66/2 (3)
Summer (July-Aug)
<100 mm 57/7 (12) 21/0 (0)
100-200 mm 61/21 (34) 12/6 (50)
>200 mm 1/0 (0)
Total 119/28 (24) 33/6 (18)
Fall (Oct-Nov)
<]00 mm 9/1 (11) 4/1 (25) 21/1 (5)
100-200 mm 28/7 (25) 2/2 (100) 16/0 (0)
>200 mm 29/10 (34) 35/16 (46) 32/3 (9)
Total 66/18 (27) 41/19 (46) 69/4 (6)
No relationship between fish size and inci-
dence of L. cyprinacea infection was apparent.
Infection site on the exterior surface of the fish
was usually near the fin base (buccal and oper-
cular cavities were not regularly examined). Of
271 copepods seen, 32% were associated with
the dorsal fin, 24% with the pelvic fins, 21
with the pectoral fins, 13% with the anal fin,
2% with the caudal fin, and 8% with other body
parts. Mean intensity of infection was 1.7 co-
pepods per infected fish; 63.6% of 162 infected
fish hosted one parasite; the maximum number
was seven.
Recapture of Tagged Humpback Chubs
Recaptures of tagged fish included 17 of 433
(3.9%) tagged in the Little Colorado, 13 of 242
(5.4%) tagged at the confluence (C 4), and two
of 45 (4%) tagged in the Colorado. One fish was
recaptured twice from the Little Colorado, 5
and 15 months after tagging. Recaptured fish
at large from 1 day to 16 months were as much
as 17.1 km from the point of release (Fig. 6).
Thirteen recaptures, mostly from reaches LC