9425

• UCREFRP Catalog Number: 9425
• Author: Bezzerides, N. and K. Bestgen.
• Title: Status Review of Roundtail Chub
• USFW Year: 2002.
• Copyright Material: NO

between these different-sized streams (Bestgen 1985). Brooder et al. (2000} found

' between 7,267-26,903 eggs in 4-7 year old females, 27027 mm TL, from the upper
s at
seven da
t
f
ft
y
o
our
er
Verde River. In the laboratory, hatching of embryos occurs a
I9 °C (Muth et al. 1985}.
Hybridizartion. As previously mentioned, taxonomic status of CRB Gila has long
been confused and h bridization suspected among putative forms (Jordan 1889, Ellis
Y
1914, Everhart and Seaman 1971, Kaeding et al. 1990). Several factors including spatio-
ral oven of s a ,occurrence of mature fish with morphologic
tempo ap P Ong
characteristics intermediate between putative parental types, and hybrid crosses made in
the hatchery provide strong evidence for hybridization between G. robusta and other Gila
sp. (Vanicek and Kramer 1969, Rinne and Minckley 1970, Hamznan 1981, Valdez and
Clemmer 1982, Kaeding et al. 1990, Karp and Tyus 1990b).

wl' and DeMarais 1993) have
Although genetic studies (DeMarais et al. 1992, Do uig
presented convincing evidence for widespread introgressive hybridization in Gila and
concluded that "...Colorado River Gila represent a complex of self-maintaining,
genetically distinctive species which are capable of exchanging genetic material..."
(Dowling and DeMarais 1993), disagreement among scientists exists regarding the
r taxonomic and evolutionary status of Gila sp. (Douglas et al. 1998}. Whether
hybridization, variation within and among species, or other factors are responsible for
the presence of morphologic intergrades between G. robusta and other Gila skies is
unclear (McElroy and Douglas 1995, Douglas et al. 1998).

Growth. Growth rates of roundtail chub are largely dependent on life stage, water
' temperature, and habitat. Growth of roundtail chub larvae reared at 19 to 20°C in the
laboratory ranged from 0.0 to 0.7 mm/day (Muth et aI. I985). Vanicek and Kramer
(1969} found the annual growth increment for roundtail chub in the Green River to
decrease gradually after four years of age. No difference in growth rates (lengths) were
observed between sexes. Brooder et al. (2000) reported mean annual growth rates of

Final Report SePtembei' 2~2
22