None the less it does happen and some fish do make it too adult hood. Its probably not the best example. Swordtail and platy hybrids on the other hand are easy to produce, common, and viable.If you heard about guppies and mollies breeding, then someone told you wrong. It doesn't happen often. Yes, it's possible, but not viable. A female molly can possibly have guppy babies, (a guppy can have molly babies but they usually die in frybirth) but if they're not deformed, stunted, or stillborn, they're still sterile. And they usually don't even live long enough to tell that, either.
those are very pretty fish, regardless of the fact that their mongrels. lol infact I would even venture that I prefer their appearance to both koy and goldfish.