Hi Barbara
I just joined in, and wanted to add that I too lost an "old" fish for no apparent reason. But the keyword here was apparent. I am at 3rd level Environment and all other amenities are in place. But even with those, the game seems to cycle reliably between a case of ick followed by a case of fungus (and always when you still have some of the last remedy left and need to replace it with the other
), and I had forgotten to pause the game overnight... which I'm guessing allowed one of those diseases to run full cycle and killed the fish.
Fortunately, I try to keep good notes (eh, that is...sticky notes everywhere, trips to the combination page, plus numerous hours fiddling with my own spreadsheet) so I was able to breed that fish again.
I must say, I've not been this involved with a game since the first "MYST" came out eons ago. I absolutely love it!