Researchers in Japan recently found that if they kept the fish in a tank that was full of water with different things dissolved in it, they could create a more female-dense population. The use of actual female hormones is not allowed for animals being raised for human consumption, so the researchers explored isoflavone, which is a chemical that's found in soybeans. They isolated a compound called genistein, and this is derived from isoflavone. Sure. And they found that if you had a tank of water with 400 micrograms per liter, this resulted in a tank of catfish that were 100% female.