Black Chinned Livebearer

I bought some of these fish a while ago and i think that the females might be pregnant but i dont know for sure. Can someone tell me how long the gestation period is or what water parameters the fish need to breed?

Keep alone, with other hardwater or brackish fish, or with unrelated livebearers. They like brackish, hard water - like most livebearers. Add a tiny bit of sea salt (you won't need much!) and some crushed coral in small quantities to bring up the hardness. Be certain, beyond certain, that there is NO ammonia in your water when you begin to increase the hardness. Make all changes gradually, over the course of a few days.

Lots of daphnia and algae to nibble at is generally a good idea, but not always necessary if your food is of highest quality.

Lots of water changes also helps encourage more frequent fry drops in most livebearers I've worked with.