it looks like some kind of toadfish (Psychrolutidae).
What's the signage like at AQWA? I noticed in your photos that even the seahorses don't seem to have been adequately labelled for identification. Certainly their website is rubbish in that respect (although to be fair, most public aquariums have rubbish websites if you want to find specifics on what they hold).
This particular fish was in one of the aquariums in the entrance area, which had no labels at all. Only Shipwreck Coast had "conventional" labels. The other parts all had signs like this.
Mostly you had a bunch of pictures of some(!) of the inhabitants at the bottom and the rest was just not signed at all.
Even the species-specific signs were just: Sea Snake, Cone Shell, Stone Fish without scientific names or anything.
That's so poor. I do understand that it isn't possible to have labels for every species in an aquarium because there are so many mixed tanks and so many invertebrates, and tank inhabitants get swapped around a lot, but how difficult is it to put specifics on a sign for the tanks' main inhabitants?! To me, that level of ineptitude at education is both baffling and totally unacceptable.
I had a further look around on their website. The Education page, as expected, was mostly about school visits (no other visitors need education), but on the side of that page is a link for "Creature Features" which at least has some fact-sheets for selected species. AQWA-The Aquarium of Western Australia | Perth Underwater Adventure » Education
From those I found that the seahorses there are West Australian Seahorse Hippocampus subelongatus. The sea snakes are, um, just Sea Snakes...
@Chlidonias looks like Batrachoididae, not Psychrolutidae. Both families are called toadfish (as well as others like Chaunacidae and some members of Tetraodontidae).
