7119 ‎(2)‎

• UCREFRP Catalog Number: 7119
• Author: Emery, L.
• Title: Physiological effects of electrofishing.
• USFW Year: 1984.
• USFW - Doc Type: February 3-4, 1984.
• Copyright Material: NO

crevices when shocked, making them hard to see and difficult to collect. Other species that
are pelagic are not easily captured by electrofishing because-they stay in waters that are
too deep to be electrofished. Species that exhibit territorial behavior are easily captured
because .they are not normally frightened by an approaching electrofishing operation. By
targeting a species, the collector can do things to improve the chances of collecting them
by electrofishing. For example, by increasing the pulses per second on a backpack shocker,
one can collect smaller fish that would normally not 6e collected.
loo
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Teal lenafh In Inches
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110
100
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fe/e1 length (~willimeter,)
Figure 2. Percentage of marked trout of Figure 3. Relation between recovery time
various lengths recaptured with
230-volt, 2500-watt, direct- measured in seconds, and total
current electrofishin length of common shiners (Adams
g gear et al. 1972).
(McFadden 1961).
Resistance, or the ability of individual fish to conduct-electricity, varies greatly among
species. The res istance of a fish. acts to reduce the voltage gradient that it encounters
from head-to-tail, and it is that change in gradient that is needed to make electrofishing
possible. Normally a head-to-tail gradient of from 0.1 to 1 V/cm of fish is required to
collect fish with an electrical current. The resistance of various species affects their
ability to 6e collected with electrofishing gear. The four species listed in Table 1 show
a range of res stivity (Halsband 1967).
Table 1. Calculated resistances for various types of fish (adapted from
Halsband 1967).

Species
Resistance (ohm/cm)
Trout
Perch 818
Carp 981
Gudgeon 1,149
1,228
The trout has less resistance than the carp and is thus more susceptible to electric cur-
rent. The higher the resistivity of a fish, the more current it can absorb without effect.
Resistance can also change with temperature. Table 2 shows how the resistivity of carp
CAL-NEVA WILDLIFE TRANSACTIONS 1984
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