Yes David R,
Don't mention them on this forum.
I believe you have to have a permit to keep them, and it's illegal to keep,
breed or sell them or shift them from any water way,
or pond, or lake, in NZ.
If you catch them from a lake, you can not [legally] return them alive again to the water.
So,
Why not just get a whole lot of guppy females and breed them.
They aren't vicious like the gambusia, which by the way is their tax. name.
Alan