Hey Devaler,
bad news! I finally found a nice and realistic solution for an
animated fish but it is soooooooo slow.

You can download and view it at this address:
http://www.mojocafe.de/test.swf

If you open that address within your Device and put it in fullscreen
you can see a fish swimming.
If you test that url within an usual PC you will realize how fast
it realy should be

So at the moment: no aquarium... sorry.

Carlos