There is a possibility that Endlers may hybridize with several related species from the Poeciliidae family of livebearers including Mosquito Fish (Gambusia), Mollies, Swamp Guppies (Micropoecilia picta) or other livebearers.
Hybrids produced from these pairings are likely to be sterile. However hybridization with fancy or wild type guppies is quite easy and will produce fry that are fertile able to produce hybridized fry.
Because crossing Endlers with guppies is so easy most hybrid Endlers available today are produced from Endler / Guppy hybridization.
Crossing Endlers with fancy guppies can help breath new life into weak strains. These hybrids often have some of the iridescent colors that Endlers are known for.
Although Endler hybrids are frowned upon by some they are highly sought after by others.