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

650 MESA AND SCHRECK
20 HATCHERY
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TIME (h)

FIGURE 3.-Mean feeding and aggression rates for hatchery (upper panel) and wild cutthroat trout (lower panel)
before (pre) and for several hours after they were electroshocked, marked, and released in an artificial stream. All
trials within a group are combined. Asterisks denote rates that are significantly lower than the pretreatment rate (P
< 0.05). Vertical bars represent 1 SE.
return to normal (except at 7 h) during the obser-
vations (Figure 3).
Small sample sizes precluded statistical analysis
of feeding and aggression data by hierarchical rank
of fish. We therefore present the data in a quali-
tative context. Dominant hatchery fish were gen-
erally feeding normally by 2 h posttreatment,
whereas aggression was low for the first 3 h post-
treatment and highly erratic thereafter (Figure 4).
Feeding rate in intermediate hatchery fish showed
no appreciable changes, although aggression rates
were generally lower than the pretreatment rate
during much of the observation period. Subordi-
nate hatchery fish showed no real changes in either
feeding or aggression. Feeding rate of dominant
wild fish was appreciably lower only during the
first hour after treatment, although the fish did
maintain a slightly lower rate of feeding until 24
h posttreatment (Figure 4). Intermediate wild fish
did not return to normal feeding rates until the
second day, whereas subordinates showed no ap-
preciable changes in feeding rate except during the
first hour after treatment. After electroshocking
and marking ended, rates of aggression generally
remained low for wild dominant and intermediate
fish throughout the observation period.
Physiological Experiments
Electroshock plus marking.-Because there were
no differences in overall mean levels of cortisol
between trials with fish that were shocked once,
or shocked and marked, we combined all data.
Mean concentrations of plasma cortisol of shocked
and marked fish increased immediately after
treatments and reached a peak at 1 h (Figure 5).
They returned to control concentrations at 3 h,