Kellen and Sarah Wessenbach, owners of White Brook Tilapia Farm, are extremely knowledgeable about all aspects of tilapia rearing (and other fish types), and are themselves aquaponic gardeners. When I saw a response Kellen gave to a question on Murray Hallam’s forum about how to manage fry population explosions in tanks with male and female fish I asked him to do a guest post on this subject. I think you will find this fascinating…
Tilapia Breeding by Kellen Wessenbach, White Brook Tilapia Farm
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.
So… in the average home aquaponics system, even a single female could have a tank filled to the brim with young tilapia in no time at all… perhaps just a single spawn! Interestingly, the juveniles from previous spawns will actually be the most cannibalistic fish in the tank. Young tilapia have a huge appetite for high quality protein, and tilapia fry are a great source of protein in their eyes. They’ll eat any sibling they can fit in their mouth… something worth keeping in mind if you are actually trying to grow out some of them. Grading by size is literally a full time job at our hatchery. You have many options when it comes to preventing excessive spawning and/or recruitment. Here are a few:Increase adult fish density – Crowded tilapia rarely pull off successful spawns. Males prefer to have some room for their nest area. They will chase off anyone they consider intruders. In a heavily stocked tank, they are too busy chasing non-spawning fish away from their nest site to have much time to actually pull of a spawn. Further, even if they do manage to court a female and get her to release eggs in the nest site, the huge population of non-spawners will attempt to swoop in and eat the eggs… and they’ll do so with great success. Of course, you’ll need to increase bio-filtration capacity to suit any increase in fish density, and you still need to keep in mind that all tanks have a maximum carrying capacity at some point.
High densities can be risky. A lot more risk for water quality parameters to turn south quickly.
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.
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.
Separate the male and female tilapia: This obviously works, however, it can be pretty time-consuming in large systems, and only works as well as the person’s ability to correctly ID the sexes. In most home systems, it’s not a huge deal to handle 50-200 fish though. Stock single sex fish – Stocking “all male” fish for instance. Just keep in mind that hormones are used to produce “all males” unless they come from a genetically male cross. Since most aquaponics folks are growing their own food to avoid hormone treated foods, this doesn’t usually jive with our goals.
Reduce light: Tilapia spawn less frequently and less successfully when provided with more dark hours than light hours. Reduce temps slightly. Tilapia tend to spawn at optimal levels at temperatures between 78-84F degrees. At 72, most strains virtually stop spawning all together, though they also grow slower… so not really the best solution in most cases.
Personally, I like the idea of using predator fish. It’s not a fail proof method by any means, but it works well enough to control the population, and it can be a lot of fun too. 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.