I have a pair of swordtails. I have had them for two months. They are breeding great. The first time they had young I did not get the female in the net breeder in time. She gave birth again two days ago. I did have her in the net breeder this time. I was able to get about 40 fry transfered to my breeder tank this time.
Swords will have young about every 28 days depending on temperature and other water conditions. It is hard to see the gravid spot, but you will notice that she is more "plump" then normal. I will try to get the female in a net breeder about a week before she is due. If you know when she had her last bunch just add 28 days onto this to get the next due date.
They will have the young early morning, right after you turn on the light. Try to get the young out ASAP because she will eat what she can. Keep in mind also there will be still born fry. Do not worry this is normal.
I have my swords in water that has a PH of 6.5 and a temperature of 84. I know this sounds extreme but they are in with discus.
Most females will have about 30-50 healthy fry. This can very depending on the size of the female. Some large females could have over 100 young!!
Good quality Swordtails are getting hard to find. I hope this will help anyone who is thinking about raising swordtails.