hello there.. just want to share my experience with swordtails
a year ago, i had 8 (1male and 7 females) given to me by e neighbour
i did put them in a pond heavily planted with cabomba(fanwort) and some unknown pondweeds.. i also did put a lot of rocks for future fry to hide in..
right now i think i have hundreds of em in the pond... i think that the pond is overstocked already so every month.. i take about 15-30 of em... find some willing takers.. and if i dont find any i would have to feed em to some of my carnivorous fish (sorry swordtail lovers.. i need to do this in order to save the other ones from the pond crashing or something)
in breeding, i think it is important to have floating plants.. new born fry tend to swim up the surface.. the adults will try to eat em most of the time so its important to have hiding places for em... hornwort is good for that just like tricksterpup said... after a few days... the fry will start swimming to the bottom so its good to have some hiding places in there too in the form of rocks or small caves... the adults will stop chasing them eventually when they start to have some coloring in them (probably because they would be bigger than the adults' mouths i dont know really

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if u r planning to breed em in ur aquarium, maybe u need some pre-filter sponge of some sort to avoid having the fry sucked into it...
and btw, these things can grow, some of mine are abt 4-5 inches long already... i dont know the maximum size, maybe u can ask tricksterpup, he knows a lot about livebearers
gud luck