I would love to see a data tracker that allows you to see the fish you have "discovered". When you unlock a level (type of fish) it could show you a "?" for the fish in that group you have not found. This would not leak info for the people you like the mystery, but would serve as record keeping (and save paper). It could be as simple as a photo album of fish. You don't get the "album" until you get the first fish that would be in the album.

If possible, a true screen saver where you could add the fish from your discovered files to screen saver tank. This could serve as a personal "trophy tank" that was not part of the game play.