22
GPP ELECTROFISHER
USER’S MANUAL
2016
ALTERNATING CURRENT
Alternating Current (AC) is an
electrical current in which the
direction of current flow reverses
a number of times per second.
In an AC field, the fish takes
a position transverse to the
electrical field lines and attempts
to face the anode and cathode
successively, in rhythm with
the AC cycle. When the field
strength increases, tetany occurs,
and the fish is stunned. Strong
contractions of the body muscles
make the fish feel rigid.
At high voltages, the larger
fish may be killed, the muscular
contractions being so severe
that vertebrae are fractured and
the brain damaged. Hence AC
electrofishing is only successful
with small fish in low conductivity
water.
DIRECT CURRENT
Direct Current (DC) is the term
given to electrical current that
flows only in one direction. The
current flows from the negative
electrode (cathode) to the
positive electrode (anode).
The reaction of fish to direct
current is quite different from
their reaction to alternating
current. The first reaction of the
fish is to turn toward the anode
and start to swim toward it until
it reaches an electrical field
strong enough to stun it. Being
stunned is called galvanonarcosis.
The severe muscle contractions
caused by AC do not occur, and
the fish recover much faster.
Mortality rate is much lower with
direct current.
PULSED DIRECT CURRENT
Even greater anode attraction
is possible with pulsed direct
current. Pulsed direct current is
made by interrupting steady DC
with an electronically controlled
switch. The switch gives several
on-off pulses per second. The
number of pulses per second
(pulse frequency) and the on
time (pulse width) have different
effects on different species of
fish.
In a pulsed DC field a fish’s
body flexes with each pulse,
and returns to normal between
pulses. This flexing and
straightening accentuates the
involuntary swimming towards
the anode, called galvanotaxis.
Smith-Root Programmable
Output Waveforms give you
complete control over your
electrofisher output. This
patented method of synthesizing
waveforms makes it possible to
produce virtually any waveform,
so you can select the one that is
safest for the fish. POW allows
you to create narrow pulses
to achieve the same results as
wide pulses. Narrower pulses
put less power into the water.
This has three benefits: you have
less chance of damage to the
fish, your battery or fuel lasts
longer, and you can work in very
conductive water that overloads
conventional electrofishers.
RESPONSE OF FISH TO DC
FIELDS
straight flexed straight flexed straight
+
0
off on off on off
Galvanotaxis: In pulsed DC a fish's body flexes with each pulse.
As the fish nears the anode it receives a very high head-to-tail volt-
age.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
50
280
18
30
6.25
9.5
Field Intensity, V/cm
Distance from anode, m
Voltage across fish
120
4 0 0
70
40
22
12.5
6.25
TYPES OF CURRENT
