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The request by Giuseppe Maio for information on saltwater electrofishing is
a common question. The problem, of course, is high electric current demand
on the equipment, brought about by the very high ionic concentration of
salt or brackish water. The answer is to reduce the current demand as much
as possible by using pulsed direct current, the pulses being as small as
possible. For example, if pulse duration is reduced to 1 or 2 milliseconds,
and pulse frequency is kept below 30 hertz (pulses per sescond), this will
allow the operator to increase the amplitude, or height, of the pulses with
the voltage control. Fish generally respond best when the peak voltage is
higher and the average voltage (area under each pulse curve) is lower. If
the fish don't respond, then average voltage is increased (i.e., pulse
frequency and/or pulse duration) is increased until they do respond. It is
usually better to increase frequency first, followed by duration.
Ultimately, none of this may work if the power source (generator) is
inadequate. In this case, one can experiment with smaller electrodes
(reduced surface area) to further reduce the demand for current. If smaller
electrodes don't work, then only a larger generator (more watts) will do,
and even then, this may not work if the fish are very resistant to
electricity. Generally, fish with heavy scales are quite resistant; also,
small fish are more resistant than large fish of the same species.
Jim Reynolds, Unit Leader
Alaska Cooperative Fish and Wildlife Research Unit
University of Alaska Fairbanks
Fairbanks, Alaska 99775-7020
USA
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