Have to say IMO just about any FH can be fertile, even white eyed kamfas. It all depends on the fish. I know several people who have successfully bred white eye kamfas. The catch is waiting for the fish to mature. Male FH usually mature very slowly. Females can spawn as little as 3", however some males take over 2 years to reach sexual maturity. Also one thing I have noticed is that 80% of all FH from overseas are infertile. My theory of this is that foreign breeders add a chemical solution to the water which causes infertility. The reason for this is simple. To protect their trade. If you think about it all there income comes from people spending ridiculous amounts of money to import fish from their farms. If they sold fertile males everyone would breed them and they would lose all their business. Thats my theory anyway, however I will attest that all male FH reach sexual maturity at different ages/sizes. The only real way to tell is trial and error and to just wait and see. I had a large 8" male ZZMalau that I tried breeding about 5 times with several diff. females. Nothing happened and I assumed he was infertile. About 6mo. later I tried again and BAM. I now have some wicked ZZmalau fry. Good Luck Bro!
Bump