I have a 600 gallon IBC system, without anything on the bottom of the ibc's. I got 30 golden tilapia fingerlings in May 2013. They have been doing very well, they are about 5-6" long and getting very fat. My water temp ranges between 75 and 70 F. From what I read, tilapia don't anything more than warm water and they will breed like crazy. Is that correct?

I thought I would have had some new fingerlings being born by now since just a month ago my water temps were in the 80's and the fish were pretty big then too. My system is built into the ground so I can only see the tilapia from the top, and I can't tell if any are holding eggs from that perspective. Do they need anything else (gravel, hiding places, etc.) to breed or should I be fine as is? Any help would be appreciated, I don't want to start eating any tilapia till I have some new ones growing in the system.

Thanks