7706

• UCREFRP Catalog Number: 7706
• Author: Mesa, M. G. and C. B. Schreck
• Title: Electrofishing mark-recapture and depletion methodologies evoke behavioral and physiological changes in cutthroat trout
• USFW Year: 1989
• USFW - Doc Type: Transactions of the American Fisheries Society
• Copyright Material: YES

BEHAVIOR AND PHYSIOLOGY OF MARKED FISH
individual fish means. After testing for homoge-
neity of variance, we found no differences among
hatchery trial grand means by one-way analysis of
variance (ANOVA, P < 0.05); therefore, all data
were pooled to calculate a single pretreatment
grand mean. Because of problems encountered
with using two disproportionately large fish in one
trial, only two of three wild fish trials were con-
sidered experimentally sound. When a two-sam-
ple t-test revealed no significant difference be-
tween the grand means, the data were combined.
The pretreatment grand means and posttreatment
hourly rates were then compared: we subtracted
the hourly posttreatment rates of feeding and
aggression for each fish from the corresponding
pretreatment grand mean. Within each time in-
terval, we summed these differences for individual
fish and ;used a one-sample t-test (for use with
equal or unequal variances) to determine whether
the average difference for the group at that hour
differed significantly from zero (i.e., null hypoth-
esis: no difference between pretreatment grand
mean and hourly posttreatment means). For any
hour, if the null hypothesis was rejected (P < 0.05),
we concluded that the pretreatment grand mean
for rates of feeding and aggression and the post-
treatment rates were different. Data were com-
pared within hatchery and wild groups, between
groups, and within a hierarchical ranking based
on dominance matrices of aggression received and
elicited. We also compared food intake between
individuals, and made general behavioral obser-
vations of each fish.
Physiological experiments. -Cutthroat trout (56
± 1.1 g) used to evaluate the physiological effects
of electroshock and marking were obtained from
Alsea (Oregon) State Fish Hatchery; cutthroat trout
(18 ± 0.32 g) used to evaluate the effects of mul-
tiple electroshocks were obtained from Cedar
Creek (Oregon) State Fish Hatchery. All fish were
transferred to the Oregon State University Smith
Farm research facility and held in circular tanks
(0.9 m in diameter) receiving flow-through, aer-
ated well water at 12 ± 1 °C and exposed to a
natural photoperiod. Fish were fed Oregon Moist
Pellets daily and acclimated for at least 2 weeks
before each experiment.
To assess the physiological effects of procedures
for mark-recapture studies, we used a completely
randomized design with three treatments. A group
of 35 fish distributed in three tanks received a
single 4-s electroshock (300 V DC from a Coffelt
model II-A backpack unit). We subjected another
group of 35 fish distributed in three tanks to the
647
same electroshocking treatment; these fish were
then captured, anesthetized with tricaine, weighed,
measured, marked as in the field study, allowed
to recover in buckets, and returned to their orig-
inal tank. As a control, 25 fish in two tanks were
left undisturbed. We collected five fish from each
group immediately (<I 0 s) after and at 1, 3, 6,
12, 24, and 168 h posttreatment. Control fish were
sampled alternately between electroshocked
groups. The fish were rapidly removed from the
tanks with dip nets and placed in a lethal dose
(200 mg/L) of tricaine. The fish were then re-
moved from the anesthetic and bled from the cau-
dal vasculature (after the caudal peduncle was sev-
ered) into a capillary tube coated with heparin
ammonium. Plasma was obtained by centrifuga-
tion and stored at -15°C for future assay. A sam-
ple of five fish generally required less than 5 min
to process. We conducted this experiment twice
during February-March 1988.
To assess the effects of multiple electroshocks,
we distributed 45 fish into two tanks and exposed
them to three consecutive 8-s, 500-V.-DC electro-
shocks separated by 0.5 h. Forty fish in each of
two other tanks received only a single 8-s 500-V-
DC electroshock. Because fish in this experiment
were smaller than those used in the first physiol-
ogy experiment, we increased the voltage and
shocking time to elicit a similar electronarcotic
response in the fish in the two experiments. Con-
trol fish were as described previously; in addition,
we subjected 30 fish to an acute handling stress
that consisted of netting the fish from the tank,
holding them in the air for 30 s, then returning
them to the tank to recover. Our objective was to
compare stress responses between electroshocking
and acute handling. We obtained plasma samples
as described previously at the same sampling in-
tervals; we also collected samples 30 min after
shocking and handling and immediately after each
successive electroshock. We conducted this ex-
periment twice during October-November 1988.
Plasma cortisol was determined by sH-radioim-
munoassay (Foster and Dunn 1974), as modified
by Redding et al. (1984) for use with salmonid
plasma. Plasma lactic acid was assayed by fluo-
rimetry (Passonneau 1974). All data were tested
for homogeneity of variance (Bartlett's test: Sokal
and Rohlf 1981). Homogenous data were ana-
lyzed by either a t-test or ANOVA followed by
Fisher's least-significant-difference test at the 5% ^a
probability level (Ott 1977). Data with heteroge-
neity among variances were tested by a t-test for
means with unequal variances or by a Kruskal-