Coming from the Murray-Darling district, these pests have always become fertilizer and never released.
However, before you go sticking them in your garden, here's an interesting alternative. A couple of local fishos have found salted carp fillets to be their #1 bait for some very big snapper. These blokes head inland for a week, catch kill and fillet these mongrel pests and convert them into 'baked snapper'.
Cheers
Hodgey