We have swordtails and platies living in cold water here in the south west of Western Australia. We find them in the wild (people release them here) and we have had them in ponds. At the Karrakatta cemetery, they have a few ponds there and they are full of beautiful looking green swordtails. We catch Xiphophorus variatus platies in the upper reaches of the Swan River in Perth. ll these areas have water temperatures of 3-5C in winter and up to 30+ in summer.