A conventional fish tank is probably boring for its inhabitants. Why not give them something to do to keep their minds occupied? Let them play Pac-Man with this fish tank built by Instructables member antoniraj. He made it with 5 mm sheets of glass for the outside and 2 mm sheets for the maze. He sealed them together with Araldite epoxy glue.
Now he just needs some Siamese fighting fish to act as ghosts.