That's great that you like the game so much. There are a lot of us that are addicted to these games. By the way, I like Myst, too!

As for the diseases - some of them can be really hard to spot on certain fish. Ick, in particular is difficult to see, especially on fish like the Spotanus. I've had fish die overnight because I didn't see that they were sick, and by morning it was too late!