Emaciated Red Platies

[FishOCD]

After giving birth twice, my female red platy's tail fin became narrow (vs. more fan shaped). Then, despite eating well, her belly became impossibly concave and she died. That was many months ago. Now some of her offspring have developed the same problem. One has already died. (Other breeds of fish in the tanks are unaffected. Several red platies unrelated to the original female are fine.) Any ideas as to what this is and what I can do to stop it?

PS: There is no sign of ich or "orange blobs" that some others have posted regarding sick platies.

 

[Strikh]

I've had my blue platys dropping like flies. They are the offspring of other blue platys in my tank. Oddly enough, the parents are doing fine. It's only the 3-month old fry that are dying. None of the other fish in the tank are showing any bad signs at all -- thankfully.

I've been led to believe that it's a product of too much inbreeding. Seems that lots of people are having lots of platy problems over the past few months. The hatcheries are being blamed by many. I'm still a rookie at this hobby, so I don't really know. I'm just repeating what I've read/heard.

 

[Blackpearl]

My platy didnt have the orange blob thing too, and it died like 3 weeks ago So far my other fishes haven't been infected with it, so I think it was caused because of cross breeing rather than tuberculosis. Later on, my friend told me that the fish was actually a mix between platy and swordtail :?

I dont know what you can do with them. I just separated the fish to another tank and leave him there until he eventually died. Maybe it's best to euthanize but I didnt have the heart...

Here are other threads with similar problem
http://www.aquariumadvice.com/viewtopic.php?t=25206
http://www.aquariumadvice.com/viewtopic.php?t=22932
http://www.aquariumadvice.com/viewtopic.php?t=23438