I bought two swordtails a male and a female about three months back. A month and half ago I realised the female swordtail was heavily pregnant and so I setup a smaller 12 litre tank added a sponge filter (to prevent any babies being sucked up into the filter) a heater and found some plastic mesh which had holes large enough for the fry to drop through the holes of preventing the mother swordtail from eating the newborn baby fry.
This mesh was placed in a n shape with the edges touching the sides and bottom of the tank preventing the mother from being caught in it.
I also placed in the same tank a couple of pregnant mollies for company.
One day I came downstairs and saw something dart across the tank. It was a baby orange swordtail. I left the mother in the tank for a couple hours to make sure she had dropped all her fry and put her and the other fish in the main tank after acclimatising them of course.
Catching baby fish is very difficult so to count them and move them to a nursery tank that I setup I used a turkey baster. It doesn't harm them at all.
After doing a fry count I had 14 healthy baby swordtails and today they are about a month old and have been moved into the main tank along with some baby silver mollies. Non of the baby fish died. I made sure their water was in good condition and fed them crushed up fish fakes three times a day and removed any unbeaten food with the multi functional Turkey baster.
As I am writing this my female swordtail is again in the hatchery as she is heavily pregnant again and will give birth this week sometime. This time she has a pregnant yellow guppy as a friend.