You don't have to just have your aquatic friends on a table in a 5 gallon glass tank any more. You can have them in your toilet (an idea that my sister Chelsea actually slavaged a toilet to accomplish as a sculptural peice. She got as far as painting it silver and glittery, making a collage inside the seat lid that read "Where all good fishies go" with arrows pointing down the commode. And there were still-life fishes headed down the commode, but we never quite replaced the water tank with a real fish tank).
Or in an old computer (methinks these flat screens and laptops these days won't quite cut it, though).
And so on...
Oct 24 EDIT: I just saw this one, too, for those who want a small fish hemisphere on their walls.