CAT WISE:

In a greenhouse nestled in a valley near Half Moon Bay, California, farmer Ken Armstrong is tending to his herd, some 3,000 fish who are key members of a complex ecosystem that also includes some helpful bacteria and these floating leafy greens.

There's not a speck of soil to be seen here at Ouroboros Farms, where Armstrong and his colleagues are growing produce with an agricultural system called aquaponics.

KEN ARMSTRONG, Owner & Founder, Ouroboros Farms: The fish are the integral part of a system. They provide the nutrients for all — for the system. So we feed our fish an organic fish feed. And this is — becomes the nutrient base for all of our plants.

So, the food that the fish eat becomes usable nitrogen by the plants. And so the fish are actually the engine of growth. This is where all the magic happens.