8021

• UCREFRP Catalog Number: 8021
• Author: Bestgen, K. R. and J. M. Bundy
• Title: Environmental Factors Affect Daily Increment Deposition and Otolith Growth in Young Colorado Squawfish
• USFW Year: 1998
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

112

BESTGEN AND BUNDY

temperature was constant at 220C or fluctuated
around that level (Figure 4). However, otolith
growth was maintained through starvation in both
temperature treatments. Before starvation, somatic
growth was slightly faster with fluctuating tem-
perature (mean, 2.3 mm TL) than with constant
temperature (1.9 mm), but it was similar in the 6-
d period after feeding was resumed (means = 1.5
mm versus 1.4 mm). Otolith increments were of
relatively high contrast before, during, and after
the starvation period.
In experiment 3, food was withheld from 6-d-
old fish for 5, 10, 15, or 17.5 d to determine effects
of the starvation period on otolith and fish growth.
During the first 5 d of starvation (to age 11 d),
otolith and somatic growth rates of larvae in all
treatments remained similar to those of continu-
ously fed control fish (Figure 5). Fish in the 5-d
starvation treatment showed a delayed effect of
starvation in that their body lengths and lapillus
diameters were smaller than control values at day
16. In the 10-, 15-, and 17.5-d treatments, somatic
growth was largely arrested by the time fish were
11 d old, but otoliths continued to grow in fish up
to day 21. After feeding resumed, somatic growth
of fish in the 10-, 15-, and 17.5-day treatments
increased immediately, but it did not reach the
control rate until fish had fed for 2.5-5 d. Con-
versely, otoliths grew only slowly or not at all for
the first 2.5-5 d of resumed feeding; after 5 d,
otolith growth was nearly that of controls.
Width and contrast of otolith growth increments
was not reduced during the first 5-d starvation pe-
riod. However, the space on the otolith correspond-
ing to starvation periods longer than 5 d was gen-
erally opaque throughout and daily increments
were more difficult to distinguish. Daily incre-
ments deposited after fish resumed feeding were
dark and of high contrast, but that quality was
apparent only 1-2 d after the starvation period.
In the absence of food, a temperature difference
of 70C had little effect on otolith growth (exper-
iment 4). After 7 d of starvation, lapillus diameters
of 21-d-old larvae averaged 148 fLm (SE, 5.3) for
the 180C treatment and 152 (3.5) fLm for the 250C
treatment. When fish were fed continuously
through day 21, lapillus diameters were 173 (5.3)
fLm at l80C and 206 (1.3) fLm at 250C. The food
X temperature interaction was significant (ANO-
VA: F = 12.95; df = 1; P = 0.0024).

Discussion

Otoliths were present in Colorado squawfish
embryos prior to hatching in all the 18, 22, and

260C temperature treatments tested. These tem-
peratures represent the known range over which
Colorado squawfish successfully spawn (Nesler et
al. 1988; Tyus and Haines 1991; Bestgen and Wil-
liams 1994), suggesting that all wild Colorado
squawfish larvae should have otoliths prior to
hatching.
Daily increment deposition in otoliths of Col-
orado squawfish was verified for larvae reared in
all fluctuating and constant temperature regimes
from 18 to 260C, a range that approximates tem-
peratures expected in the wild. Otoliths from fish
reared at a constant temperature were more diffi-
cult to age accurately than those from fluctuating
temperatures. Similarly, Campana (1984) and
Neilson and Geen (1985) found that plainfin mid-
shipman Porichthys notatus and chinook salmon
Oncorhynchus tshawytscha, respectively, deposit-
ed daily otolith increments in both constant and
fluctuating temperature environments, but that in-
crements were of higher contrast in fish reared in
fluctuating than in constant temperatures.
Only dark, high-contrast increments were count-
ed in this study. Occasional problems with lighter,
lower-contrast, subdaily increments were reduced
by keeping the microscope focal plane near the
middle of the otolith. Dark, high-contrast otolith
increments should be present in wild Colorado
squawfish because water temperature in the wild
exhibits regular daily fluctuations, reducing the
potential for deposition of nondaily increments
and for age estimation bias.
Temperature may affect otolith and somatic
growth independently due to temperature-medi-
ated rates of fish metabolism (Mosegaard et al.
1988; Wright 1991; Bradford and Geen 1992) or
complex temperature interactions with the endog-
enous circadian rhythm of otolith calcification and
matrix deposition (Secor and Dean 1992). In this
study, otoliths were smaller in fish reared at l80C
than in fish reared with constant or fluctuating
220C or fluctuating 260C, suggesting a positive re-
lationship between temperature and otolith growth
independent of somatic growth rate. However, a
direct influence of temperature on otolith growth
could not be demonstrated because the colinear
effect of temperature on somatic growth of Col-
orado squawfish (Bestgen 1996) could not be re-
moved.
Fast- and slow-growing Colorado squawfish
showed differing relationships between body
length and lapillus diameter indicating that so-
matic and otolith growth rates were not propor-
tional. Separate relationships of total length or oto-