9721

• UCREFRP Catalog Number: 9721
• Author: Brouder, M.J.
• Title: Age and growth of roundtail chub in the upper Verde River, Arizona.
• USFW Year: 2005.
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

[Note]

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December
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Sectioned
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system (EPIX, Inc.; PIXCI software) consisting of
a personal computer, video monitor, and camera
equipment connected to a compound microscope.
Otoliths were viewed under oil immersion at 40X
magnification using transmitted light. Measure-
ments were taken from the nucleus to the outer
edge of each opaque band and from the nucleus
to the margin or otolith radius.
Age and growth.~ Three independent readers
counted the number of annuli on each cross section
and assigned ages accordingly. When discrepan-
cies occurred, all readers reread the otolith and if
the readings still disagreed, the otolith was dis-
carded. Precision in age estimates among readers
was determined by calculating a coefficient of var-
iation (CV == 100 X SD/mean; Chang 1982).
Length of roundtail chub at previous age was
back-calculated from otolith measurements using
the modified Fraser-Lee method and a biologically
relevant intercept (Campana 1990) because the
size of fish and otolith at swim-up were available
from hatchery-reared fish used in the validation
component of this study. The biological intercept
method is based on the assumption of a constant
linear relationship between fish and otolith length
within an individual. Deviations from this as-
sumption using the biological intercept, which
uses a biologically determined intercept value, are
less problematic in the calculation of annual
growth than the traditional Fraser-Lee method,
which uses a statistically estimated intercept value
(Campana and Jones 1992). Back-calculated
length at age was determined using the following
equation:

La == Lc + (00 - Oc)(Lc - Lo)/(Oc - 00),

where La is the back-calculated length to annulus
a, Lc is the length of fish at capture, Lo is the length
of fish at swimcup (8.5 mm), 00 is the otolith radius
at annulus a, Oc is the otolith radius at capture,
and 00 is the otolith radius at swim-up (0.1243
mm). Because t-tests did not indicate significant
differences between male and female lengths at
age, data for both sexes were combined to back-
calculate growth.
Growth rate of roundtail chub was determined by
fitting the von Bertalanffy growth model to back-
calculated length-at-age data. The model is

L, == L~[1 - e-K(Ho)j,

where L, is the total length at time t (years), L~ is
the maximum theoretical attainable total length
(mm), K is the growth coefficient, and to is the

NOTE

867

time (years) when length theoretically would be
zero (von Bertalanffy 1957). Model parameters
were estimated using the computer program FISH-
PARM (Prager et aL 1989).
Otolith validation.- To validate opaque bands as
annuli and to determine time of annulus formation,
otoliths from roundtail chub collected monthly
from January through December 1997 were ex-
amined, and mean marginal increment data (dis-
tance from the last annulus to the edge of the oto-
lith) were plotted against month of capture. To
further validate the use of otoliths to age roundtail
chub, adult fish were collected from the upper
Verde River in March 1997 and transported to Ar-
izona Game and Fish Department's Bubbling
Ponds Fish Hatchery in Cornville, Arizona. Brood-
fish were artificially spawned, progeny were raised
in the laboratory. and fry were reared outdoors in
an earthen pond. Approximately 50 roundtail chub
were collected annually in late June to early July
for 3 years using a fyke net, measured for TL (mil-
limeters), and sacrificed. Otoliths from known-
aged fish were removed and aged using the same
procedures as wild-caught fish. In addition to val-
idating annul marks on sagittal otoliths of known-
age roundtail chub, daily increments on otoliths of
age-O roundtail chub were validated by comparing
the age (in days) with the number of rings on their
otoliths.

Results

Age and Growth

A total of 312 roundtail chub, ranging in length
from 50 to 415 mm TL, were collected from the
upper Verde River (of which 280 had otoliths that
were legible), aged with a 96% first-time reader
agreement, and measured. Among-reader preci-
sion (CV) for wild-caught roundtail chub otoliths
was 8.2. Ages of roundtail chub ranged from 1 to
7 years, the oldest fish from the upper Verde River
population having completed seven growing sea-
sons. Two distinct cohorts of roundtail chub were
sampled in both 1998 and 1999. The majority
(44%) of fish collected in 1998 were age 5 (1993
year-class) followed by age-3 fish (36%; 1995
year-class). Similarly, roundtail chub from the
1993 and 1995 year-classes (age 6 and age 4, re-
spectively) comprised the two highest percentages
of fish collected in 1999 at 42% and 28%, re-
spectively. The longest and heaviest fish collected
was a 427 -nun TL, 836-g, age-7 female; the largest
male (age 6) was 413 mm TL and 629 g.
Mean length at age did not significantly differ

".