All the time! At least I think they're mating.
Anyway, the behavior usually takes place in the evening, after feeding. My male Bimac will choose one or two females and 'shimmy' around her while both ascend and descend rapidly through the water column (my tank is 36" deep, btw). Then suddenly, he will 'strike' and it's over, except the part where every other fish in the tank will then gather around to eat what must be her released eggs. Very cool to watch...I mean, to observe. Yeah, observe. :hmm2: