Text taken from GBAdev.org:

This is my 1st attempt using multiple backgrounds to produce that parallax SNES effect. Use the D-pad to move the fish around.I used DEvKitAdvance to compile the code. Feel free to use the code for whatever you want. My apologies for lack of comments, documentation and efficient code. Thanks to Dovoto for the GBA tutorials! They are very helpful.

http://www.gbadev.org/