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It's a ruddy gurnard perch (Neosebastes scorpaenoides). There is a website devoted to identification of Port Phillip Bay fishes. I'll track down the link for it and post it for you.
Just took a look at the website, and it's not quite as comprehensive as I thought. It's also a little tricky to navigate unless you already have a rough idea of the fish species. Anyway, it might prove useful for future identifications: Port Phillip Bay Taxonomy Toolkit.