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cyberdelic

Controlling tilapia population

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I'm curious what methods APHQ members use for controlling their fish population.

Here in Florida -- as far as I've been able to determine -- it seems that I'm limited to Blue Tilapia. Hybrids and other variants are prohibited. That seems to rule out breeding hybrids to favor primarily-male fingerlings.

I've read about treating with hormones and whatnot, but I'm curious what other methods are out there and what results others have had with them.

One technique I read about involved using netting of some sort about an inch from the bottom of the tank, which was supposed to keep the females from being able to get to the eggs once they are released. Since it was listed on the page of someone trying to sell fingerlings, though, I was a bit skeptical. Does such a method actually work or would I be better off searching for some fish-sized condoms and forcing the juvenile fish to watch re-runs of MTV's "Teen Mom"?

Would keeping some predatory fish stocked in the tank be more hassle than they are worth?

Just evaluating my options... I don't currently have a system set up yet, but overpopulation is one concern that I wanted to work out the logistics of ahead of time.

Thanks.

--Kevin

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Not really a problem with a high stocking density, yes you will have slower growing females and the occasional fingerling pop.

A few predatory fish such as bluegill or catfish seem to work wonders at slowing down population explosions.

In a home system it's not really a problem, but could be an issue with a commercial setup.

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I think the tilapia do a decent job of population control. I have had 3 hatching's, but can only find a few of the most recent hatch. The young tilapia are eating the new born fry, and the great part of that is, it is free food to the young fish.

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Predator fish actually work quite well when stocked in appropriate numbers and correct sizes. Netting on the bottom of a tank works okay, but it can cause issues with solids removal in some situations and can often become a bit of a pain with regard to maintenance in general. Fish cages inside the tanks work better in my opinion, and make harvesting and examining very convenient if built and installed with that in mind. High stocking densities tend to help a great deal as well, for several reasons. One, it's difficult for males to "claim" a nest site and defend it constantly. Two, when spawning does occur, non-spawning males and females tend to swoop in and gobble up a large percentage of the eggs. Three, tilapia will prey on their own and high densities tend to also equate to very limited hiding spots for fry.

Methyltestosterone is the primary hormone used for sex reversal. I have serious concerns regarding the safety of it, though mainly because of exposure concerns for workers handling it at hatchery facilities rather than the finished product (though many consider that a huge concern too).

If you want to try a bit of a DIY sex reversal method that does not involve hormones or hybridizing, simply keep your nursery tank of fresh swim-up fry at a temperature of 98F for a couple of weeks (otherwise operate normally). This has been demonstrated to produce anywhere from 70-99% males in several studies. However, survival percentages usually fall to about 50-70% during treatment. For a backyard grower, the reduced survival rate is of little concern usually, because you still have plenty of fish to restock systems.

Hope that helps!

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Predator fish actually work quite well when stocked in appropriate numbers and correct sizes.

Nice! Yeah, that certainly seems to be the consensus.

Netting on the bottom of a tank works okay, but it can cause issues with solids removal in some situations and can often become a bit of a pain with regard to maintenance in general. Fish cages inside the tanks work better in my opinion, and make harvesting and examining very convenient if built and installed with that in mind.

What's the typical size of the openings of a cage and wouldn't it have similar drawbacks as the netting?

If you want to try a bit of a DIY sex reversal method that does not involve hormones or hybridizing, simply keep your nursery tank of fresh swim-up fry at a temperature of 98F for a couple of weeks (otherwise operate normally). This has been demonstrated to produce anywhere from 70-99% males in several studies. However, survival percentages usually fall to about 50-70% during treatment. For a backyard grower, the reduced survival rate is of little concern usually, because you still have plenty of fish to restock systems.

Interesting. Will keep that in mind.

--Kevin

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What's the typical size of the openings of a cage and wouldn't it have similar drawbacks as the netting?

Hi Kevin,

With regard to mesh size, 1 inch is pretty ideal for caging 5 inch or larger fish. If you start fingerlings out in cages, 1/8 inch or so will be needed, but would not be ideal for long term use or housing larger growouts because of the likelihood of them collecting solids, bio slime, etc. and then ultimately restricting flow in and out of the cage. Netting on the bottom of a tank can tend to cause solids to accumulate under it. Suspended cages allow the solids to escape to the tank and continue on to your drain without as much risk of obstruction.

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I can't give advice, only my own experience.

I've had my tank running for a little over a year with this batch of fish. (My first batch died of a pH imbalance before they were big enough for breeding to be a problem, so I can't give data from that.) I'm in CA, so similar weather to yours.

I have a fairly high stocking density, and I have a good sized algae-eater (plecostomus) in with the fish. He's probably 1.5 lbs.

I have zero breeding happening.

I don't know if it's the temperature, the density, or the plecostomus. I can only say it isn't an issue for me. If it becomes one, I'll have to make other arrangements I suppose.

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Plecos are egg hogs. They will swoop in and eat eggs during a spawn at every chance they get. Since they are well armoured, they don't tend to be bothered by a tilapia trying to defend their nest. They tend to do a really good job of interrupting/preventing spawns.

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Thanks, kellenw. I knew I could count on you to explain it!

So in the interest of clean tank, I backed in to a great method of population control. Cool.

And most importantly, this would probably be a simple solution for cyberdelic to use. And anyone else who wants to stop their tilapia from breeding. It's sure a lot easier than suspending mesh from the tank floor. (And it's easy enough to move them to an isolation tank for a month if you *do* want to allow a period of breeding.

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Hi,

I'm curious what methods APHQ members use for controlling their fish population.

The best way to treat surplus fish biomass is to incorporate it into the food chain for another species......be it fish, chickens, ducks, pigs, etc.

Gary

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Great suggestion, kellenw! I know adding a couple Plecos will up the O2 usage and waste production a little bit and not give me the yummy ROI that tilapia would, but it seems like they'd be worth it -- to keep the tilapia in check.

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