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The Boys Had Babies!

July 12, 2010

Last week a professional photographer came over to take product shots of our new AquaBundance system.  Since it was a bit of a drive for him he and his wife decided to make a day of it and brought their young son.  He was of course instantly drawn to the fish, and as he peered into the tank he exclaimed “look at all the babies!”  “Impossible” I thought.  “I have all male tilapia stock”.   But I humored him by looking into the tank myself.  I’ll be damned.  Floating on the surface of the tank was a miniature school of about 30 tiny fish.  Those boys had babies!  Here is a quick video of the babies, and our new aquaponics nursery set-up for housing them.

As background, most tilapia that are raised in this country are male because males grow bigger, faster, and reproduction is just plain messy, no matter what the species.  Babies lead to fighting, territorialism and the tank quickly gets over populated.

There are primarily two methods in use in the U.S. today to insure all male tilapia stock.

Gemetic Male Tilapia

How GMT (Genetic Male Tilapia) works. Image credit:

The first, most frequently used method is called Direct Hormonal Sex Reversal.  Basically the young fry boys and girls are flooded with male hormones at an early age causing them to all grow up to be boys.  The second method, and the one I find more palatable, is called Genetically Male Tilapia (GMT).  Basically a Super Male is produced with YY chromosomes (i.e. two male chromosomes) so when he reproduces he can only produce another super male or a male.  Hopefully this wonderful graphic from, will help explain what is going on.  They also have a much more detailed explanation of how all this works on their website – just click  on the image to go there.

Last December I got 100 “all male” tilapia that had been sexed using GMT, but since the inventors claim that the process is “95% effective” I guess I shouldn’t be surprised that a few girls slipped in.  For now I’m enjoying the babies and the fact that Mother Nature always seems to find her way around our efforts to thwart her.

2 Comments leave one →
  1. July 16, 2010 6:58 am

    This is really very interesting. I guess this is the first time that I have read something about this…I really never thought that this process of reproduction can be possible with the GMT method. That’s really amazing! Now, your aquaponic system will never ran out of healthy fish that can help feed your plants, and as a result, you can produce the best crops all the time 🙂

    • July 16, 2010 10:37 am

      It is kind of amazing, isn’t it. The funny thing is now that I have started talking about this I’ve found out that lots of aquaponic people have had similar experiences with baby fish suddenly showing up. Not a big problem at this scale, but I can imagine the chaos if half your fish were having babies!

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