If I put some guppies and swordtails in the same tank, is it possible that they will crossbreed? Or will they just stick to breeding with their own kind?
Nope they'll still breed with their own species, i have heard reports that platies and guppies if there are say only guppy males and only platy females they may interbreed but if you have mixed sexes they don't even consider it.
Also platies and swordtails will quite readily interbreed which is why many "platies" you buy grow long tail extensions!!
William is right Shimanocono,if you want to see some positive guppy crossbreeding,you have to put some endlers in your guppy tank.Endleers look alot like wild guppies,only more colorful.Those two species would definately not hesitate on having sex with each other