Ray These are the same questions the state would ask as well.
I would propose that they legalise the import of koi above a certain value/size/quality. This would inhibit the buyers of cheap fish from purchasing them for the novelty value and then discarding them. Killing all fry would likewise stop the millions of culls produced by hobby breeders for gaining access to the Australian ecosystem. Possibly a ban on fish under a certain size, say 40 cm. It might even be able to chemically sterilize all imported fish but I'm not sure.
Fish leaving the pond by any means is a potential threat. I can imagine a bird of prey plucking a fish from a hobby pond and then finding it too heavy dropping it in another body of water. Not a likely scenario, but not impossible. So the owner must be responsible. He must make sure that the fish he owns are protected for predators and possibly even thieves. Micro chip each fish and all owners must have proper paperwork. If not
Fines, big ones! It must be proven to the authorities that no fish will escape
ever. It the same breath every pond must be located in place where there is no danger of flooding and the contents of the pond coming in contact with natural bodies of water. Thus ponds will need to meet strict criteria.
In the eyes of the state anyone owning koi will basically be possessing a bio hazard and you must never have it loose. It is the state that must be satisfied not the hobbyist. The choice is to belay the fears of the government and the green lobby or see your hobby disappear.
B.Scott