The size and shape of the gravid spot can vary depending on the number of embryos that the female is carrying. A female who is carrying a large number of embryos may have a gravid spot that is large and round, while a female who is carrying a small number of embryos may have a gravid spot that is small and oval.
The gravid spot is a helpful way to tell if a female yellow molly is pregnant. It is also a way to estimate how far along she is in her pregnancy. The closer the gravid spot is to the anal fin, the closer the female is to giving birth.