21
GPP ELECTROFISHER
www.smith-root.com
LOW CONDUCTIVITY WATER
Distilled water is a very
good insulator. It has a
conductivity range of 0.5 to 5.0
microSiemens/cm. If a normal
voltage is applied in distilled
water, very little current will
flow. Power flow is too low to be
effective for electrofishing.
The current passing through
a fish decreases as the power
flow decreases. To get the same
response from fish, the current
can be maintained by either
increasing the voltage, or by
keeping the resistance low.
If a higher voltage is used, up
to 1,200 volts may be necessary.
High voltages create three
problems, special electrical
equipment is required, safety is
reduced for the operators, and
conditions are lethal for fish close
to electrodes.
The resistance can be kept
low by increasing the size of the
electrodes. The only limitations to
this are the availability of larger
electrodes, and the weight of
electrode that can be handled by
the operator.
HIGH CONDUCTIVITY WATER
High conductivity is over
2,000 microSiemens/cm. If a
high voltage is applied, most
current will flow easily through
the water and the fish will
hardly be affected. The electric
current follows the path of least
resistance and bypasses the
fish completely. Therefore use
low voltages and high currents.
Currents as high as 60 amps
are common, the limiting factor
being the rating of the power-
supply.
Some brackish water and
industrial waste water have
conductivities over 10,000
microSiemens/cm. Here smaller
power-supplies are unable to
deliver enough power to stun
fish. Waters in this range can only
be electrofished effectively with
the larger model GPPs.
The Smith-Root 7.5 GPP
outputs 62 amps through 8
gauge stranded cables. This unit
can stun large fish in the interface
between fresh and salt water. For
example, Striped Bass can be
stunned for taking brood stock.
Theoretically high conductivity
could be dealt with by using
smaller electrodes, but this would
reduce the range and also create
damaging current densities near
the anode.
FISH CONDUCTIVITY
A fish will receive the maximum
shock through its body when
the conductivity of the water is
the same as the conductivity of
the fish’s flesh. Unfortunately,
this is rarely the case. Generally,
fish conductivity is around 115
microsiemens/cm.
FISH SIZE
Among fish of the same species,
the larger fish are more sensitive
to electrical currents. Fish absorb
power as a function of body
surface area. This is important to
remember if you are shocking for
small fish and large fish are also
present. The large fish are going
to receive a much greater shock
than the small fish.
TEMPERATURE
Water conductivity increases
with temperature.
SUBSTRATE
Certain bottom substrates will
conduct electrical current. These
weaken the electric field in the
water, making fish capture less
effective.
ADJUSTING THE VOLTAGE
By adjusting the output voltage,
the effects of the water’s
conductivity on electrofishing
can be reduced.
The current flowing through
the water is directly related to
the voltage applied. The higher
the voltage, the greater the
current will be.
When adjusting the output
voltage the major consideration
is the power being used. This
is especially true for battery
powered electrofishers. Power is
equal to the voltage multiplied
by the current. When figuring the
power for an electrofisher, the
fact that it is usually putting out
pulsed DC must be taken into
consideration. The instantaneous
power during a pulse may be
quite high, but if the electrofisher
is only producing pulses at a 25%
duty cycle, the average power
would be approximately 25% of
the instantaneous power.
INTRODUCTION TO ELECTROFISHING
