Thanks guys. That is exactly what I needed to know.
I chose these two out of the six in the aquarium because they were very friendly to each other, and one of them was excavating the nest. The second nest got covered in yesterday. The other four fish were rather aggressive towards these two, so that is why I chose these two.
There obviously was not a spawn, as both fish are still eating voraciously.
I'm now thinking of introducing two additional fish to the tank to increase my chances of success.
I've looked at a number of the tilapia, and I from the reading I've done, I cannot see anything to differentiate a male from a female.
