Are you sure this isn't P. volitans or an intermediate phenotype between it and P. miles? The two species are nearly identical (differing only in ray counts of the pectoral, anal and soft dorsal fins), and P. miles does not occur in Australia - most are intermediate phenotypes.
I don't think this individual is identifiable to species from this image - it has 14 pectoral fin rays, which doesn't help much to distinguish them - P. miles always has 14 pectoral fin rays, and P. volitans can have 13 or 14 (14 is more common). Do you have a photo of this individual (or any other lionfish in the tank) that clearly shows the soft dorsal and/or anal fin? The ray count in these fins is more diagnostic.
