7112

• UCREFRP Catalog Number: 7112
• Author: Minckley, C. O.
• Title: Fishes of Arizona.
• USFW Year: 1973.
• USFW - Doc Type: Arizona State University,
• Copyright Material: YES

i

a
97 s
r

seem to have evolved organs of attachment, but instability of bottoms
and channels in the primitive Colorado must have dictated development
of an active, aggressive, body form and function. Vanicek & Kramer
(1969) reported G. elegans occurring principally in eddies and pools of
the Green River, Utah, stressing that they were never taken in swift
currents. However, during flooding, and in crossing swift channels, the
body form must certainly be functional, despite the habitat preferred
during periods of normal discharge. Individual G. elegans that inhabit
lakes of the lower river, such as lakes Havasu and Mohave, retain their
streamlined body shape, and apparently occupy an active, limnetic niche
in the reservoirs.
Little is known of the early life history of the bonytail chub.
Vanicek & Kramer (1969) treated all chubs shorter than 200 mm in total
length as one population in their studies on the Green River (involving
therefore a mixture of G. elegans and G. robusta). Spawning by the spe-
cies has been recorded, however, in Lake Mohave by Jonez & Sumner
} (1954). A group of about 500 fish concentrated over a gravelly shelf in as
much as nine meters of water. Each female was escorted by 3 to 5 males, k.
.and eggs were simply scattered over the bottom. Observations were made
in May. In the upper Green River, bonytail chubs apparently spawned in
June and July, on the basis of occurrences of gravid females in collections
and the appearance of young, at water temperatures of about 18° C
(Vanicek & Kramer, 1969). Young of bonytail in streams presumably be-
have similar to other chub species, moving to the margins to feed and
grow, then progressively invading deeper and larger waters.
Adult bonytail in the Green River feed primarily on terrestrial
insects, plant debris, and algae. Young feed mostly on aquatic insects.
In lakes, bonytails feed on plankton and algae, on the basis of a few
'stomachs examined.
Gila elegans from the Green River grow to at least seven years of
age, and achieve lengths of more than 350 mm and weights of almost
0.5 kg (Vanicek & Kramer, 1969). The largest seen by me, caught by an
angler from Lake Havasu, was almost 50 cm in total length (48.9 cm).
This species appears to be hybridizing extensively in the vicinity of
Lake Powell with both the Colorado and humpback chubs. Specimens
of Gila from that area are especially valuable, and should be carefully
preserved and submitted to qualified persons for study.
~:

z
t