You guys makes it so confusing.
In the old day when Thailand have not exported fh yet. Most of the fh that comes into the states are from Malaysia. Malaysia exporters will only send out males and no females. The males are fertiles but what good will it do when there is no female to reproduce.
Back then, blue dragon, jks were very popular and once in a while, hobbyist would get lucky and get a female fh and she would fetch a very high price.
When the Thais exporter starts selling fh, they imported males and females but some of the females are not fertiles. I do not know what they did to them but my guess is hormones in the feeds. My friend and I imported 10 red dragon females and we split up the fish and out of 10, only 2 manage to laid eggs after keeping them for almost 1 year. I do not import fh anymore but I get females here and there from thailand and they were fertile.
The only male fh that I know is infertile is kamfas, since I do not have any experience with king kamfas. I have heard that kamfahs will be fertile when they get older. I am guess this is because of the fish that they use to breed kamfah are more fertile when they get older. I use to keep a lot of kamfahs because of their colors compared to zz but I never kept them long enought to fully mature to find out if they are indeed fertile at a later age.