1201

• UCREFRP Catalog Number: 1201
• Author: Bulkley, R. V. a. R. P.
• Title: Temperature Preference and Avoidance by Adult Razorback Suckers
• USFW Year: 1983
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

604

BULKLEY AND PIMENTEL

with their thermal preference. No mortality oc-
curred among the razorback suckers acclimated
at 20 C and 26 C, and 20 fish at each temper-
ature operated the device.

Temperature Preference
Data used to estimate the final preferendum,
collected during the second 24-hour period,
were first examined to determine possible die I
variations in temperature selection, Means of
the modal temperatures selected by individual
fish from a given acclimation temperature were
not significantly different between day and night
(Fig. 1),
Inasmuch as die I variations in temperature
preferences were not statistically significant, day
and night data were combined for estimation
of the final thermal preference. Means of in-
dividual modes ranged from 22.7 C to 29.0 C
(Fig. 1). Differences in final preferendum esti-
mates of fish from the four acclimation tem-
peratures were statistically significant (analysis
of variance, P < 0.01). Fish acclimated to 14 C
preferred a significantly higher final tempera-
ture than did those acclimated to 20 and 26 C
(Fisher's LSD test).
Data from the fish acclimated at 20 and 26 C
provided the most reliable estimate of the final
thermal preferendum for the razorback sucker.
Both groups had essentially the same mean
modal temperature preference (22,7 and 23.1
C; mean = 22,9 C) which is midway between
their respective acclimation temperatures; one
criterion for final preferenda is equality of ac-
climation and preferred temperatures (Rich-
ards et al. 1977), As a second estimate of the
species' final preferendum, the geometric mean
of the thermal preferenda for the four temper-
ature-acclimation groups was calculated to be
24.8 C. The actual value for adult razorback
suckers evidently lies close to 23 C and between
22 and 25 C.

Discussion

One explanation for the higher temperature
preferred by the razorback suckers acclimated

--1

FIGURE I.-Distribution of temperatures occuPied by ra-
zorback suckers during their second 24 hours in a shut-
tlebox. Data are observations made at 15-minute inter-
vals, pooled Ol'er 4-20 fish originally acclimated to 8,
14,20, or 26 C.

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Day ~
25.1
Night I I
8 C, N = 4 25,0
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25
Mean
of
20 Modes
-I SD j +2 SE
15 j I I
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L Range of J Day
10 Night
Modes
5
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10 20 25 30
28,2
Day I
28,4
Night f--- I
29,0
25 14C,N=10 Combined I .J..
20
15
10
5
1'0 1'5 2'0
22,7
I I Day
22.3
25 I I Night
22.7
20 I I Combined
15 20C,N=20
10
5
22.8
I I Day
25 22.3
I Night
20 23.1
I jo
-1 Combined ,
15
10 26 C, N = 20 J
5
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10 15 20 25 30
TEMPERATURE OCCUPIED IC)