The larger talipia has taken all the rocks from one end of the 50 gal aquarium and spit them into a pile. Is this to create a swept area for eggs or just fish boredom activity? If it has to do with mating is this a male, female/ or either activity?
Both male and female will create a 'nest'. Keep an eye on this one and see if it pairs up with any female(s). If he/she choose to mate, the female will have a mouthful of eggs and will not eat during the incubation phase.
You might also be interested in my reply to MikeH here: http://community.theaquaponicsource.com/forum/topics/my-tilapia-are...
The fish I believe to be female is the fish that can't close its mouth. Show in my "Talipia can't close mouth" post. I think they mated and she couldn't keep the eggs and the gold fish in the tank with them ate them.
I am not really trying to raise Talipia. It is just my curious observaion.