In all likelihood this is Spotted Parrotfish (Cetoscarus ocellatus) rather than Bicolour Parrotfish (Cetoscarus bicolor). Both were formerly considered a single species, but has since been split - C. bicolor is now considered a Red Sea endemic. It wouldn't be impossible for an Australian aquarium to obtain a true C. bicolor, but it is far more likely this is the Australian taxon C. ocellatus.
