Ideal temperature/tank requirements for encouraging livebearer pregnancy

[emeraldking]

It depends on the kind of livebearer you're talking about what the ideal breeding temperature is. In your case with platies and swordtails (I'm assuming they're fancy ones and not wild) a range of 20°C-28°C will be good. It really doesn't have to very high to get them to breed.
There are also livebearers that will only breed better or totally at lower rates. Even with a large number of wild swordtails or even wild platies which belong to the socalled northern Xiphophorus species prefer lower temperatures. The southern Xiphophorus species prefer higher temperatures. But there are way more livebearers that produce better at lower rates. That's why I've mentioned that it really depends on the kind of livebearer species which breeding temperature is preferable.

 

[Aussie_Bristle]

I am still finding little fry from one of my bearers giving birth the other day. I have found using your phone torch and looking for them at night is a lot easier. I have hornwort on one side but I find they like to sit around my group of elodea that I have tied in a knot and placed in my be if my corners of the tank. I have only got a few from the clutch as my Rosy’s eat the fry as soon as they can find them, doesn’t matter how much I feed them they are always hungry and eat everything, they are known for their over eating.

 

[EllRog]

I currently have a number of platies, mollies, and a swordtail in a 55g community tank with a number of other fish set at 78 F. Is this an ideal temperature to encourage pregnancy or should I increase it to 79 or 80 degrees? I'll likely place any pregnant fish in a breeder net and then transfer the fry to a separate tank. I'm just kinda looking for something to invest my time and energy into during the quarantine.

I had great success at 82F, had it at that temperature before lowering to 80 once all the females in my tank were pregnant or had just dropped. I just fed well, twice a day, 6 days a week, had the tank stacked with plants (real and fake) and made sure I had 1 male to every 3 females. Produced Platties, Guppies and Swordtails. Didn't do anything very different to normal to be honest, didn't do water changes any more frequently, they just breed like crazy!