Hi this is a very interesting topic and very helpful. I would like to ask a question also, I have 4 female guppies and 2 males. The females are having the black pregnancy spot every now and then which after few days it's changing to red and after few days back to black, but they are not having any fry. In the aquarium I also have some plants. Anyone knows why the pregency spot is changing colours and no fry are being born?