Wow, How do you have feed available 24/7 ?
Rainman already answered the way it's done on the commercial side with the belt feeders, and they work great let me tell you.
A good alternative method, IMO for home growers, is to grow fry and fingerlings in greenwater. You still feed as frequently as you can, but in between feedings the tilapia will browse on the algae. This helps offset the reduced feeding frequency when you aren't available 24/7 to feed them or don't have a belt feeder due to cost (they are somewhat expensive).
I actually tested this method myself this winter by splitting up offspring from the same male and female into two separate tanks. One had cultured greenwater and the other was clear water. The fish were fed the same amounts at the same frequencies. The tilapia in the greenwater tank grew nearly twice as fast as the ones in clear water.
