The music file (canonguitar.sgt) is built into the Marine Aquarium program, so it's not contained in a folder. It's still there in the latest version. Just press M when the Aquarium is running to hear it. It's a MIDI version of Pachelbel's Canon that I wrote, and uses a single MIDI instrument, a guitar sample that I created. This way, the music can be compressed down to almost nothing (back when saving bytes was still considered important).
