Gravel?

I'm just setting up my first system. Our tilapia fingerlings arrive later this week, so I've been studying like crazy. I've been reading about the care and breeding habits, etc of tilapia -- it doesn't seem too different from the oscars I used to have in my tropical tank.

One source mentioned that in the courting ritual, the tilapia make a "nest" in the gravel. I wasn't aware that most people used gravel in their AP system.

Can somebody give me some insight into this?