I had this happen to my platy tank and I lost all of them because I tried treating for everything, which stressed them out and no response. The platies had fry that did not seem to get sick and I had transferred them, about 15, to a 10 gallon tank. Out of all 15, only two survived to adulthood and are still alive and very healthy. Happened during the summer and I sanitized the entire tank because I feared it was TB. My platies looked EXACTLY like that and because it was untreatable I assumed it was TB. Now, because I've had open hands in the tank and have not contracted it, I don't believe it was TB, though I may just have a good immune system. I think it may be a species specific disease but I have not found any info on what this disease was. No wasting away occured but they became emaciated so TB was probably not a problem especially because its so rare and no other symptoms occurred. If any other fish begins to look like that, my advice would be don't treat, just quarantine.
I love my platies, but I know that they get inbred and inbreeding can give rise to strange ailments.
