Now, it would be cool if the desktop could actually be a 3D layer and those fish were simming around in the background in realtime...
Dude have you ever heard of DreamRender? Probably the most amazing and incredible program I have ever seen.
Your desktop is basically a screensaver and you can download hundreds of different ones. Best of all, this is all done with little to no CPU time.
http://www.dreamrender.com/
Christ it's amazing. I'm not sure if they have a fish one though