Fertilty in hybrids is a tricky thing, to produce a fertile male the two species being crossed need to be very closely related. Take for instance Herichthys cyangutattus and Herichthys carpintis, very closely related, very likely to produce a fertile male off spring. Kamfas (most fh actually) come from crossing Amphilophus to Vieja, or Paraneetropolus as they're now known. Paraneetropolus and Amphilophus aren't very related at all, because of this there's some amount of genetic incompatability. This can cause things like infertile male offspring, low number of fry, and so on. My theory on fertility in FH is that once they hit somewhere in the 65%-75% purity range they start being fertile. Say you breed an FH with tons of Amphilophus species in it, (midas, trimac, lyonsi) that means it's got mostly amp in it, has red eyes, and because most amps are very closely related, is very likely fertile. Kamfas are usually bred with not enough paraneetropolus blood to be fertile, not to mention the paraneetropolus complex just isn't as intertwined as Amphilophus. They probably have approximately 60% paraneetroplous blood and 40% amphilophus blood, neither species has enough of a "controlling interest" to carry the fertility. If you knew which paraneetropolus (or something very closely related) was used in your particular fh you could just back cross to that species and have a fertile male. Say your kamfa has heavy syn blood, if crossed back to a syn or melanurus the male fry might very well be fertile.
