Australia has 99% hard woods, so every thing is AOK.
What to look out for is soft sections in you timber, but it would be the same as using Indian almond leaves only larger scale
Some timber will leach tannin stains, this is from the process of waterlogging and it can go on for a long time, once again no issue with shrimp unless it is allowed to go unchecked.
Buying bleached timber makes no difference as the bleaching only affects the out side of the timber, the tannin comes from inside.
Water logging can take a long time and one of the best ways of water logging and stain removal, is to soak the wood in a bin or something like that and water change weekly until the stain is gone and the wood sinks.
I use to collect Mangrove stumps when it was legal and never had a issue with them and I have used river wood for years with out trouble, so long as it is hard and not to fresh its AOK, if its fresh soak it to remove the staining.
In 50 years I have not been mad aware of any reasonable common Aussie timber that is dangerous, if in doubt test a piece, if its dry no need to boil it and look out for things living in your timber.
A story for you, back when the ARK landed LOL, The first time I took my now wife on a trip it was to collect Mangrove stumps at Bribie island, we filled the boot of here Torana with timber, a few days later she was driving through south Brisbane with a friend, when a crab crawled across her friends foot, the friend jumped out of the car screaming, lucky they had just stopped a traffic lights, the friend would not get back in the car and caught a cab home LOL, she still married me