True Muppies and Gollies ARE sterile. The ones you see in LFSs today with names like MollyGuppy or GuppyMolly are simply veiltail Mollies. The science has been proven over and over conserning the viability of guppy molly hybrids. See Norton's works. Yes, there are some real ones out there. They are sterile and do not reproduce. In fact, the true hybrids are mostly obtained by a modified "invitro" fertilization, milking the males and injecting it into fertile females as the gonopodum does not "catch" properly most of the time to produce hybrids in sufficient numbers for mass production. If you are only doing this at home for your own interest you probably won't have to manipulate them yourself. Males of both species will hit on almost any female livebearer and plenty of egg layers as well!