However I am still trying to find out where I can buy feeder fish in bulk (Guppies to stay with Aust. natives). Any help would be appreciated as well as any spare Water Lilys, we are willing to come get them ourselves or if you know where to buy them (besides Tims Gardens or Garden Magic, they are very expensive).
The "guppies" are far from native, they are an introduced noxious pest....but in saying that they are well suited to your closed system circumstances.
Yes murray cod will eat things but silver perch are also quite "nippy". All large native fish are predators and will potentially injure your maron/crustaceans so just chose which ever fish you find most interesting or even a mixture. Silver perch, gold perch, australian bass, murray cod, tandanus catfish should all thrive in a pond environment. There is also a variety of small native fish such as rainbows and gudgeons, but your turt and perch will simply eat those.
I think that your turt and perch will punish your water lilies but it's worth a shot.
South Windsor Fish Hatchery (02 4572 5374) sells "feeder guppies" (gambusia), a variety of native fish, regular yabbies and a variety of pond plants including water lilies ($27.50 for a lily...a pretty standard retail price). Defiantly worth a look.
~fishbot