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>===== Original Message From Scientific forum on fish and fisheries
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>Please excuse my ignorance but I am only a minor league politician
(who is
>sending this by bcc to some major league politicians). My understanding
of
>electrofishing (other than using electricity to stun and capture fish) is
>that electricity can also be used as kind of fence for fish containment in
>open water. In other words it substitutes for the kind of pen which is
>typically used here on the BC coast. But the pens now used contaminate
the
>surrounding water. So I was asking if there are electric fences which can
>be used in open water and serve the same purpose as closed
>containers...basically aquaria.
>
>FWP
>
The original question dealt with holding tanks for fish captured during
electrofishing operations. The originator of the question used aeration in
a a closed tank system, wanted to use a larger tank, and wondered if
compressed air would work for aeration. I suggested going to an open,
continuously circulating system which, in my opinion, is superior to closed
systems for fish recovery and sidesteps the compressed air issue
altogether. The question of electrically-charged pens is not related to the
original question because holding tanks in electrofishing operations are
meant to isolate fish from electricity and allow them to recover.
However, the "pen" comment does bring up another approach: using
metal-mesh, small pens in the water body (as opposed to on land or in a
boat) to hold fish captured by electrofishing. The water inside the pen is
not electrified even though it is immersed in an electrical field. This is the
Faraday principle and it is the same rule that says you won't be shocked if
you're sitting in your car when lightning strikes it. The metal-mesh cage
allows flow-through, eliminating the need for a water pump, and the cage
can be either stationary or floating along shore, or suspended from an
electrofishing boat. The metal-mesh cage is not used very much because
it is less robust than a tank and is less moveable with fish in it. However,
it has been regularly used between the pontoons of an electrofishing raft
on the Colorado River (see Sharber, Norman G. and Carothers, Steven W.
1987. Submerged, electrically shielded live tank for electrofishing boats.
North American Journal of Fisheries Management 7:450-453).
Dr. James B. Reynolds
Emeritus Professor of Fisheries
School of Fisheries and Ocean Sciences
University of Alaska Fairbanks
P.O. Box 757220
Fairbanks, Alaska 99775
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