The one above is not full grown. The one below is closer to full grown, but I've seen them bigger.
Although they live in brackish, sometimes fresh water as juvies, they move to open ocean as adults, where the two above were caught.
I'd venture to say a 500 gallon tank would be minimal.
I was going fishing for red snapper today and we chummed some hot to the surface and they could practily feed out of our hands. I thought this would be cool in an aquarium but red snapper get huge so I was thinking about mangroves.