Well yes Gary,
The root of the Derris Plant from which they make Derris Dust is a naturally
occuring material used by natives of Asia and Oceania for stunning fish for
harvest.
In an enclosed system like a pond however, I believe the fry would succumb,
while the adults, being more tolerant, would simply be stunned.
Because it degrades so quickly, a couple of treatments would clear the whole
thing up in my estimation, leaving no trace or degradation of the pond
environment.
Soap Wort can be crushed and used too, but it takes comparatively longer as
it is an asphyxiant, and I suspect the filter would render it useless unless
turned of for the duration of the cleanout, and I am uncertain of its
afterlife in the environment.
In Australia it is illegal to keep Gambusia for the reasons the ponder is
now experiencing, and they are not fry or spawn friendly.
We use Rainbow fish and or Pacific blue eyes, which are spawn and fry
friendly, but eat mosquitos at prodigious rates, and at all stages of
development, whilst reproducing more moderately.
Just FYI for the original poster, here are some links to batbox construction
plans. This would be a better idea, as bats will consume upwards on 1000
mosquitos a night.
http://dragonet.com/bat/images/bats/
http://www.r8web.com/Boone/bat.htm
http://www.lincstrust.co.uk/facts/batbox.html
http://www.caves.org/conservancy/ikc/batbox.htm
http://www.englishcottagegardens.com/batbox.html
http://www.nrw.clara.co.uk/photosBatbox.htm

Hope this helps



"Gary Rich" wrote in message
...

Kayakkhan wrote:
Well ok...remove the Koi
sprinkle with Derris Dust (contains rotenone) the gambusia are stunned
not
killed and float to the top...scoop them out ...couple of hours the
derris
is rendered inoperative ..reinstall koi ...and any gambusia you want to
reseed the pond with
This is probably the only thing that will actually work. The bottle
trick will work to catch some of them, but I doubt it would even cut
into the breeding cycle. As you've found - they breed like tribbles.
From the way other things treat them, they must also taste terrible. We
used to have a bullfrog that would catch them and then just spit them
out. An oscar may eat them if it gets hungry enough.

Even this may not work. The fry are very tiny and easy to miss. And it
seems like there are always fry.

garyr