Two theories on way the males are infertile (i.e donkey bred with Horse will be an infertile mule). One is that is just the natural result of crossing the red devil with what ever fish they say they are useing now to get the blood parrots. The other theory is that blood parrots are treated with a chemical sertilizer by the breeders before they are shipped to the out. It seems to work only on the males if this is true because I have breed my female blood parrot to a flowerhorn twice now with live fry to show for it. I would think that the frist theory holds more water because of the females being fertile.