Taken on an artificial reef in the Coral Sea. Full of interesting rusty old crap to explore.
That's a small-medium sized QLD grouper, maybe ~ 1m -1.5m length. The hatch is a double-wide hold access doorway., so perhaps 2.5m height for scale. Viz was piss-poor that day, too. Surge kicking up a lot of particulates and plenty of micro-life clouding things out.
Some of the big groupers will go 3m in length and resemble VW Beetles. First time I spotted one of them, I nearly swallowed my reg.