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.