that's interesting.. I recently accompanied some children to a stream visit and we had a waterways person come speak to the group. As part of her talk she scoops up some pondlife, the kids count the No. of bloodworms, caddisfly larva , shrimp etc and then return it... She told us that if she finds a mosquito fish she is required to remove (kill) it or face a fine! She is not to return it to the stream. They are an introduced pest fish and they compete with inanga and are very aggressive fish that will eat eggs and even the eyes from our natives.
Gambusia (mosquito fish) are classified as Unwanted Organisms under the BiosecurityAct 1993 and People caught releasing or spreading or even selling them without an approval under the Biosecurity Act are liable, on conviction, to a fine.
SO I don't understand why there would be objection to removing them from the wild .. in order to eliminate them by way of feeding them to bigger fish.