I have lost 4 females in the last 3 months after they dropped. They did not appear very large, but dropped a small batch of fry. Afterwards, they looked completely emaciated. Their bellys were hollow, and indented. They appeared to swim OK, weren't bothered by the other fish (guppies only in this tank), and ate normally. But within 2 days of dropping, they were dead. They showed no signs of parasites, fungi, or other external disorders before or after death. The age of the fish is unknown. None of the other fish (male or female) show any signs of parasites, etc. The fry appear to be healthy and growing normally.
Any suggestions or ideas?