Live bearers are cannibals and eat their own readily. Swordtails are probably the worst but I have heard of some of the others, Guppies and Platties, being a lot less interrested in doing so. As long as there a good hiding places they have a chance. None of the Sword fry I have turned back in to my tank had a chance, even after the had grown out for two weeks. So I got the second tank!