I guess that because I have not run an installer version for some time I do not have a read me file. I have no entry under Program Files for MA3. But.. just a comment if this is in fact where the read me lives..
Is this folder not hidden for most users? Not the first place one would look..
I'm guessing that you UNinstalled MA3 at some point. The Uninstaller deletes the C:\Program Files\SereneScreen\Marine Aquarium 3\ folder (3 or 4 files), and also deletes MarineAquarium3.scr from the \Windows\System32\ folder - and that's about all that it does.
The 10d Installer asks (the normal install dialog) where to "install" MA3, and by default puts the readme.txt, the 2 Uninstaller files, and one or two other non-essential things there. Of course, you can tell the installer to "install the program" wherever you please.