It's easy to pick out the male. Female is harder. I just wait until they pair off. There is a bonded pair at HOT. That is, if they haven't been sold since Tuesday.
I don't know what specific thing triggers the spawn. I feed frozen bloodworms, black worms and do 50% WC with much cooler water. I provide several breeding sites. Usally I get the fish from HOT on one day and a week later they spawn.
I feed the fry frozen bbs and I have started hatching again.