greenterrortigeroscar said:They're Platies, swordtails are longer and the rail appears to have sword stickin out on the bottom of its tail.
BillD said:Platies (X. maculatus) are generally chunkier, than swords (usually X. helleri)as mentioned, although X. variatus platies are closer in appearance to swords, as far as body shape goes. The problem lies in the interbreeding that has been done to get the various colours available in both types. In the fish pictured, another giveaway is the horizontal lines on the body, which is typical of a brick red sword or variant.