That script removes any trace of the Aquarium from the registry, including MA1, MA2, MA2.6, and MA3, etc. You'll need your keycode or CD to reauthenticate for MA3.
I've added two additional Registry scripts if people need:
MA3 Reset Fish Settings registry script (should just cleanup the fish settings)
Marine Aquarium 3 Registry Cleaner script (should leave MA2.6 key behind)