This may be a dumb question, but if this fish is used to living at 400 feet, how can it survive in 2 feet of water in an aquarium?
Not a dumb question at all. It has to be acclimated to the lower pressure gradually and has to have it's swim bladder decompressed with a needle. Once that is accomplished it can live normally in an aquarium.
I remember reading about the procedure that has to be done to get the fish up safely from the depths it is normally found. Seems like I remember it takes a couple of days to do so.