It's a vertical animal.

But as for floor space, while it isn't a premium, a 6' x 3' enclosure is roughly what is suggested (I think 2.5 is the suggested minimum depth of the enclosure). In addition, it would allow me to see the fish in their area, and the mangrove hunting for them, or just swimming. Not to mention the whole enclosure will be substantially larger for the floor space.

Hrm... just visualize a stacked set of vivariums (the ones with sliding glass doors), but with the bottom an aquarium, the middle a normal vivarium, and the top without a bottom, just climbing area