I really hate to even bring this up but.... the lack of symptoms, followed by slight bloating, and then a quick demise, and the fact that this happens several weeks apart with the fish all displaying the same symptoms (or lack thereof).... makes me think of mycobacteriosis.
That said, I could VERY well be completely, absolutely wrong. I do not know anything about parasites, so for all I know, it could be that. And I have very limited experience with fish diseases, whether bacterial or fungal or parasitical, altogether. So it's quite possible that I'm completely, absolutely ignorant, and speaking absolute nonsense....
Unfortunately, the only way to determine if it's myco would be to send her body to a lab for analysis. Or, if you know someone at a local college or university, perhaps they could do a culture. (You could try asking for someone in the Biology or Microbiology departments.)
The first girl who died, where did you get her from?
Another alternative, which is kind of gruesome, would be for you to cut open her body. (Wear gloves if you do this, and only work on surfaces and with utensils that can be thrown away or put in a dishwasher.) If you want to do this, I recommend contacting someone who is VERY knowledgeable about diseases, and who could tell you what to look for before you try it. I mention this because I recall that someone (Basement Bettas or Coppermoon, maybe?) did this, and determined that there was an issue with the organs.
And, if this offends you for any reason, I apologize. I don't know that I could cut open a pet, myself. I'd be more inclined to bring the body to a lab if I really wanted to determine what was going on....
I'm sorry for your losses....
Last edited by LittleBlueFishlets; 04-06-2013 at 08:26 PM.