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

TEMPERATURE REQUIREMENTS OF RAZORBACK SUCKERS

603

T ABLE I ,-Mean upper and lower acute avoidance tem-
peratures of razorback suckers acclimated to four tem-
peratures. Values in a column with-a letter in common
are not significantly different (least-significant-difference
test; P < 0.05).

Accli-
mation
temper-
ature
(C)

8
14
20
26

Number
of
fish

Mean avoidance temperature (C)

Lower

Upper

27.4 a
31.6 b
27.4 a
28.2 a

8.0 a
12.2 ab
12.4 ab
14.7 b

4
10
20
20

ual fish during the first 24-hour period. Differ-
ences in avoidance temperatures among accli-
mation groups were compared by analysis of
variance and Fisher's least significant difference
(LSD) (Steel and Torrie 1960). Chi-square anal-
ysis was used to determine if the upper and
lower avoidance temperatures were experi-
enced in the first or second half of the 24-hour
period.
Estimates of final preferendum during light
and dark hours were determined from IS-min-
ute temperature readings during the 14-hour-
light and 10-hour-dark cycle of the second 24-
hour testing period. In contrast to avoidance
temperatures that were calculated as group
means, final preferenda were estimated from
the modes of temperatures occupied by indi-
vidual fish (Pitt et al. 1956; Reynolds 1977).

,.,
,

Temperature Avoidance

Estimates of the upper (acute) avoidance tem-
perature ranged from about 27 to 32 C among
acclimation groups (Table 1), and averaged 28.6
C overall. Acclimation temperature affected the
temperatures avoided by razorback suckers
during the first 24 hours (analysis of variance,
P < 0.01). Fish acclimated to 14 C avoided a
significantly higher upper temperature (P <
0.05) on the average than did fish acclimated
previously to either 8, 20, or 26 C. Lower avoid-
ance temperature estimates averaged 11.8 C and
ranged from 8 to about 15 C. Differences were
statistically significant (analysis of variance, P <
0.05). Fish acclimated to 8 C had a significantly
lower mean avoidance temperature (8.0 C) than
did fish from the 26 C acclimation group (14.7
C). Correlation between acclimation tempera-
ture and lower avoidance temperature was sta-

'.

TABLE 2,-Variation in temperatures occupied by razor-
back suckers during their first 24 hours in the shuttlebox.
Pooled data are based on 96 observations per fish taken
at 15-minute intervals,

Accli-
mation
temper-
ature
(C)

8
14
20
26

Number
of
fish

Mean
occupation Coefficient
temperature of
(C) variation'

19
21
20
20

17,1 16,7
23,5 12,0
20,6 8,7
22,3 7,6

, 100,SD/mean,

tistically significant (P < 0.01, r = 0.39" df =
52).
To determine if fish acclimated to different
temperatures demonstrated differing abilities
to eventually select a final preferendum, we cal-
culated the mean and coefficient of variation
for the first 24-hour test period from the tem-
perature occupied at IS-minute intervals. Fish
acclimated to 8 C and 14 C demonstrated great-
er variation in temperatures occupied during
this orientation period than did fish acclimated
to 20 C and 6 C (Table 2). The coefficient of
variation (SDjmean) was 16.7% for fish accli-
mated to 8 C and 7.6% for those acclimated to
26 C. These data suggest that the closer the
acclimation temperature is to the final prefer-
endum, the more rapidly fish begin to select a
final preferred temperature. Fish acclimated to
8 and 14 C were sluggish and did not move
rapidly between chambers in the test apparatus.
Low thermal responsiveness (L TR of Meldrim
and Gift 1971) was evident. Of 19 fish tested at
8 C, 10 raised the chamber temperature so rap-
idly that they died; five remained in one cham-
ber or the other without moving; and only four
regulated the apparatus successfully. Fish accli-
mated to 14 C had similar, but less severe, prob-
lems: of 21 fish, six died or jumped out of the
apparatus, five demonstrated no preference, and
10 operated the shuttlebox successfully. Maxi-
mum temperatures recorded for fish that died
in the chamber ranged from 30 to 41 C (mean =
35 C; SD = 3.7). Beitinger and Magnuson (1976)
observed similar mortality among bluegills Le-
pomis macrochirus unless maximum temperature
was limited to 19 C for the first 24 hours of the
test period. This limitation evidently allowed
the tolerance range of the bluegills to catch up