Here are some ideas, from The Aquaponic Source:
“Tilapia will reproduce to the point of danger and even overwhelm the bio-filter if your adults are well fed, and the young can find any refuge in the tank. If hungry, the adults will often cannibalize to some degree, but rarely will they control their own population. They prefer a lot of other food items over their own young if they are readily available. Non-spawning adults do have a seemingly unsatisfiable appetite for eggs though. Just one female will typically produce about 200-1000 eggs per spawn, and she’ll spawn every 4-5 weeks or so if conditions are decent enough in the tank (“decent” is pretty easy for tilapia). Even with low survival, that’s still a lot of tilapia recruitment.”
Of the total list of suggestions, the following seem the most feasible for our tanks at OMV — at least the ferrocement tanks.
- Decrease their “tank” size without decreasing total water volume – One way to do this is to use fish cages in your tank with mesh bottoms. Another way is to reduce the size of your fish tank while maintaining an auxiliary tank or sump equal to the water volume you eliminated from the fish tank. No spawning area available means no spawning taking place. (Without access to the bottom, there is no place to make a nest or lay eggs.)
- Introduce a few predator fish. The right selection will not bother your adult tilapia, but they’ll keep the “herd” trimmed for you by eating most of the young. There are all sorts of fun predator fish you could keep with them. I have a research report that concluded largemouth bass and tilapia kept in a polyculture RAS improved growth rates substaintially, compared to the monoculture control tanks of bass only or tilapia only. Similar studies have produced similar results using catfish and tilapia in polyculture systems.
“Personally, I like the idea of using predator fish…. You are able to maintain optimal conditions for fast growth, while controlling the population. For our own home aquaponic systems, I’ve used Largemouth Bass, Hybrid Striped Bass, Crappie, Yellow Perch, Catfish (they are far more piscivorous than most people realize), Oscars and Jack Dempseys… with varying results. The most successful were the Largemouth Bass, followed by Oscars and Jack Dempseys. The LMB results jive with several recent studies, but the Oscars and Jack Dempseys were purely from my own fairly non-scientific trials I did just “to see what would happen”. They worked great for me, but your results could be different than mine. The best predator fish to select are ones that have been raised entirely on live food and have never been pellet trained (you want them eating fry and small fingerlings, not pellets meant for your tilapia). That’s not always an easy fish to find.