Should my fish be breeding by now?

[Doug Johnson]

I have about 50 Blue Tilapia in my fish tank that are 6" to 8" in length. They are about 5 months old. I have some scrap PVC pipe in the tank with assorted lengths and sizes for them to hide in 

I was expecting to start seeing fry in the tank but so far nothing. What would keep my fish from reproducing?

Could it be that they are breeding but the fry are being eaten?

How about aeration? I have an air pump that really loads my tank up with air. The water literally looks like it is boiling all over the tank (The fish seem to love it). I have to turn it down in order to be able to see to inspect the tank and to check the fish from time to time. Could turbulent water be hampering reproduction?