Hi, I am Joseph... I was just wondering how long after sperm was inserted into the female, does the female show that she is pregnant or in other words the "black dot" appears in front of her "anal fin?"
It's called a gravid spot altho the presence of a gravid spot doesn't necessarily denote pregnancy. In some fish it merely shows the fish is mature enough to breed.
The best sign of fry developing is a swelling belly over a period of a few weeks from mating.
I usually just assume all females are pregnant. You can buy them pregnant usually. They hold sperm for a long time. After one batch of fry another one may be ready to brew. I assume pregnant until proven otherwise, actually.