A pregnant female can have up to 200 fry at once. The other strange thing that pregnant females can do is store sperm after they have had a brood and become pregnant later on. I have heard that they can store sperm for up to 6 months. It might actually be longer. That is why serious breaders actually use virgin swordtails, so that there is no doubt which swordtail is the father.
Swordtails are canibalistic.
Once they have their babies they will eat them given the chance. This is why some breeders use breeding traps to prevent the mother from eating their fry. So far we haven't had any luck with this technique and simply rescued the fry when we happen to see them. The males can be easily identified because they have a 'sword' on their tail, hence the name swordtail. At first I thought the sword was simply decorative, but it turns out it isn't.