20
GPP ELECTROFISHER
USER’S MANUAL
2016
distortion of the electric field is
such that the voltage near the
fish is less than it was before the
fish was present. The reverse
is true in (c) where the water
conductivity is more than that of
the fish. In this case the distortion
is caused by the current
concentrating in the water
surrounding the fish. In both (b)
and (c) not as much power is
transferred into the fish’s body as
in (a).
INTRODUCTION TO ELECTROFISHING
For many years it has been known that fish react to electric current passed through water.
Electricity was first used for fishing in 1863 when a British patent was granted. Major efforts
to apply electricity as a tool in fisheries management did not occur until after 1950. Since
then detailed studies have been made on the physiological effects of electricity on aquatic
organisms.
RESPONSE OF FISH TO ELECTRICITY
To collect fish by electrical means we must create an electrified zone of sufficient amplitude to stun fish.
In the basic electrofishing circuit, shown in Figure 1, a current is passed between submerged electrodes. A
fish between these electrodes forms part of a closed circuit and some current flows through its body.
Electrode
Water
Electrical Field
Voltage Source
Electrode
Figure 1. The basic electrofishing circuit.
0 1 2 3 4 5 6 7 8 9 10
Volts
2V
0 1 2 3 4 5 6 7 8 9 10
Volts
8V
b. Fish more conductive
c. Water more conductive
100mm
0 1 2 3 4 5 6 7 8 9 10
Volts
5.3V
a. Equal conductivities
53mm
Figure 2. Electric field patterns caused by fish.
The effectiveness of the
electrofisher is affected by
nine factors: voltage, electrode
shape, water conductivity, water
temperature, conductivity of the
stream bed, fish’s distance, size,
species, and time in the field.
If these environmental factors
are too far out of line, poor
electrofishing will result. To some
extent, the effects of changes
in water conductivity may be
compensated for by changing the
output voltage.
WATER CONDUCTIVITY
The conductivity of the water
and that of the fish’s flesh are the
factors that affect electrofishing
most.
The conductivity of water
depends on the quantity of
dissolved salts and minerals in
the water. The conductivity of
potable waters in the United
States ranges from 20 to 2,000
microSiemens/cm. Sufficient
current at realistic power levels
will flow through water in this
range to electrofish successfully.
Figure 2 illustrates the
field patterns caused by the
presence of a fish in water. In
(a) no distortion is caused by
the presence of the fish. In low
conductivity water, (b), the
