What do they do to the fish after it closes?

They feed it

They use it for outdoor fishing display purposes

I work here and the fish just stay put inside of the "aquarium" next to one of the elevators. There are fish in the small creeks on the 1st floor next to the bridge as well.

They let them fly away of course they're flying fish

They guard for ghosts.

Hope that they won't drown

I have no idea You should go in and ask them

Let them swim