Conservation & Science

Closing the loop on food production

What do worms, carp and lettuce have in common? They’re all part of an experimental food facility aiming to produce both fish and vegetables with virtually no waste, and very few inputs.

The aquarium’s Conservation & Science team recently visited TomKat Ranch Educational Foundation, an 1,800-acre cattle ranch in Pescadero, California. Founded by investor, philanthropist and climate/energy activist Tom Steyer and his wife, Kat Taylor, TomKat has become a cutting-edge model of sustainable agriculture. Ranch managers maximize the carbon-absorbing powers of grasslands by carefully migrating their cows across the land, producing TomKat’s signature LeftCoast GrassFed beef.

TomKat fish food flow chartBut TomKat doesn’t stop at ranching; it’s constantly experimenting with other forms of eco-friendly food production. A few of us took the opportunity to tour Symbi Biological, which takes its name from the principle of symbiosis: a mutually beneficial relationship between living beings. That’s a good description for aquaponics, in which farmed fish produce waste that fertilizes hydroponic plants, and the plants return the favor by filtering the water for the fish.

Bins full of worms

Doug Millar is the mastermind of Symbi, which runs under parent company InKa Biospheric. Wearing a weathered cowboy hat atop a 6-foot-3 frame, Millar takes us first to see worm bins filled with manure from the ranch’s horses. Various species of squirmy residents, from earthworms to mealworms, turn the poop into nutrient-rich compost that helps fertilize the pasture.

Worms enrich the compost that fertilizes grazing land. They, in turn, become food for fish in the aquaponic farm tanks.
Worms enrich the compost that fertilizes grazing land. They, in turn, become food for fish in the aquaponic farm tanks.

But compost is just a side benefit; it’s the worms Millar is after. They’re part of his special recipe for homemade fish food. Another ingredient is crickets, which he breeds in a hydroponic tent he calls “the hopper hopper.” The bugs live in plastic-lidded tubs outfitted with dirt trays (where the larvae incubate) and stacked egg cartons, which separate the hatched crickets so they don’t eat each other. A low-tech temperature controller keeps the tent toasty; the ranch’s solar panels help offset the energy.

What about food for the crickets? Millar makes that, too. He cultivates spirulina algae in a standard home fish tank, dries it out and feeds the powder to the bugs, turning the transparent baby crickets green.

Food for the fish

The crickets, worms and spirulina provide protein for the goldfish carp, which live in deep, round tanks in the pump room. The species isn’t on the typical American menu, but Millar’s crew once harvested about 100 and had a party, preparing them in a variety of ways. “They taste a little pondy,” Millar admits. Next time, he says, he’ll try moving the fish to a clearing tank for a couple of days before harvest.

The fish-poop-fertilized wastewater flows through PVC pipes into the crown jewel of Symbi’s operation: the greenhouse. Bright bursts of butter lettuce and bundles of basil with super-sized leaves float in polystyrene panels on aquaponic grow beds, their roots reaching through holes into the nutrient-rich water.

Compost is returned to the fields to nurture grasslands that feed the TomKat beef herd.
Compost is returned to the fields to nurture grasslands that feed the TomKat beef herd.

From there, the water – cleaned by the plant roots – cycles back to the fish tanks. The recirculation adds up to real conservation: Millar says it only takes 1.5 gallons to produce a head of Symbi lettuce. Pretty impressive, compared with an average of 13.6 gallons for a one-pound head grown on soil.

The circle is unbroken

Ranch staff serve the produce at the events they host, and Millar donates the rest to Pescadero Middle and High School to be served in the cafeteria. The aquaponics operation also produces barley, which is nutrient-rich feed for the ranch animals. And when the horses digest the barley? You guessed it: More manure for the worms, closing the loop on this sustainable food system.

Several farmed fish on the aquarium’s Seafood Watch “Best Choices” list are raised in similar recirculated aquaculture systems, in which wastewater is treated and then re-used.

“Because you’re treating the waste and capturing the waste stream, the environmental impacts we found were relatively minor compared with other production systems,” says Brian Albaum, business engagement manager for Seafood Watch.

Green-listed seafood produced with this water-wise method include U.S. farmed tilapia, barramundi, sturgeon and yellow perch. Learn more about Seafood Watch recommendations, including these farmed “Best Choices,” at

Kera Abraham Panni

3 thoughts on “Closing the loop on food production”

  1. Hi Kera,

    Good article about the basics of aquaponics!
    I could give your readers more information about the topic. I run a website called and would like to write a guest post for your blog.

    Are you okay with that?


  2. Can you go over how to cycle a system that is using tap water treated with both Chlorine and Chloramine? The Chlorine is pretty straight forward, let it sit out and the Chlorine will breakdown on it’s own and evaporate out becoming safe for the fish. However since Chloramine is a stable product how can I break it down to it’s two chemical components of Chlorine and Ammonia to treat separately and still allow the fish to be eaten. I’ve been told that using API stress coat will make the water safe for ornamental fish, but it is NOT recommended to be used for human consumption. Please Help.


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