Greenhouse-Grown Fish May Yield Bumper Crop of Vegetables Too

By Victoria Parsons 

When life handed lemons to Heather Judkins and her advanced marine biology class at Seminole High School in Florida, they grew vegetables.

An aquaculture experiment funded as a water conservation project was consuming hundreds of gallons of water in an effort to keep ammonia levels low enough for the fish to survive. “We were changing the water every week or 10 days, which was exactly the opposite of what we were trying to accomplish,” Judkins said.

A left-over grow light and hydroponics system in the chemistry lab – part of another class experiment – inspired them to create an “aquaponics” lab, a dual system where vegetables thrive in nutrients that would otherwise damage an aquatic environment.

“My class and I talked it out and brainstormed on how to reduce the ammonia while not harming the fish and we came across some information on adding the hydroponics unit,” she said. “We reduced changing the water from approximately 250 gallons every two weeks to 250 gallons every five or six weeks – the plants were soaking up the nitrogen.”

An Ideal Partnership
From a gardener’s perspective, fish and plants are an ideal partnership. Instead of fertilizing plants directly, you can feed fish – probably tilapia that are both easy to grow and tasty to eat – that then generate high levels of dissolved nutrients in concentrations that approach those in commercial hydroponic solutions.

According to studies from Louisiana State University, nitrogen, in particular, occurs at very high levels in the integrated systems. Ironically, the high levels of nitrates and ammonia are toxic to fish — but the preferred food of vegetables like tomatoes, lettuce and sweet basil.

And although mechanical problems with pumps limited the growth of vegetables in the Seminole High lab, Pasco Middle School students reaped a bountiful harvest of lettuce, tomatoes, cucumbers and herbs in an aquaponic system donated to them by Morning Star Fishermen in Dade City.

“From an agricultural perspective the vegetables are as valuable as the fish,” notes Ric Roberts, Pasco agriscience teacher. “The plants just filled the greenhouse – it really surprised me that they did as well as they did.”

Not Rocket Science
It may not be quite as simple as mixing a tablespoon of fertilizer in a gallon of water, but it’s not rocket science either, experts say. In situations where fish are the top crop, nutrients are generally generated by the fish more quickly than they can be absorbed by the plants, so water must be tested at least weekly. On the other side of the system, that means that a relatively small number of fish can support a larger growing area.

Hans Geissler, founder of Morning Star Fishermen, started the not-for-profit group to help solve world hunger. “Using fish byproducts actually lets you harvest more pounds of lettuce, tomatoes and other vegetables than fish.”
Working with students from around the world, Geissler has helped set up production units ranging from small systems in areas where electricity is so erratic that they run on solar-powered bilge pumps or windmills to large systems that feed entire villages.

Depending on your budget and your mechanical skills, you can create an aquaponic system by tying a pond kit into a commercial hydroponic system – or you can dig a pond, line it with a plastic tarp and pump water through PVC pipes planted with vegetables.

The smallest pond is typically about 500 gallons and holds about 150 fish (the rule of thumb is three gallons of water per fish). Every 10 gallons of water supports two square feet of growing area for vegetables.

Most aquaponic systems use tilapia, a warm-water fish native to Israel where it has been farmed for 2500 years, because they’re extremely fast growing, tolerate poor water quality and use a wide variety of plant-based foods. A 500-gallon tank can produce about 150 pounds of fish per year, with fish typically harvested every six months at about 1.75 pounds. Tilapia are considered to be highly efficient fish, gaining approximately one pound for every 1.5 pounds of food they are fed. In most home systems, fish should be fed commercial fish food three to four times daily, but automatic feeders are available for families who aren’t home during the day.

Systems designed to produce food typically consist of three separate chambers: a fish tank, a biofilter and the hydroponic growing area. The system should be designed so that water is pumped from the bottom of the fish tank into a biofilter where solid waste is captured. Biofilters must be cleaned weekly, and those nutrients can be directly applied to plants growing in soil. (Think home-grown fish emulsion!)

From the biofilter, water is pumped to the top of a slanted hydroponic growing area, most often constructed with PVC piping. The typical system uses an inert growing medium, such as porous clay pellets or rockwool, to hold roots in place while water moves through the system and overflows back into the fish pond.

The water in most aquaponic systems will have high levels of nitrates with lower levels of phosphate that encourages green leafy growth, so plants like lettuce, bok choy and herbs are particularly well suited. Vegetables and fruits, like cucumbers and tomatoes, can be harvested but may have more leaves and fewer fruits than those grown with more balanced nutrients.

Water should be tested weekly for pH, electrical conductivity and nutrients, but battery-powered test kits make testing simple. In most systems, 25% of the water should be changed on a monthly basis, siphoning it from the bottom of the tank to capture any remaining nutrients and biosolids.

“The Wave of the Future”
Around the world, the single most important challenge facing aquaculture operators is fish waste, which typically contains high levels of nutrients, notes Gordon Creaser, an international aquaponics consultant based in Crestview, Fla. While necessary for life, excess nutrients damage underwater ecosystems by encouraging algal blooms that block sunlight and consume available oxygen. If those nutrients are captured and used on land, however, they can provide a balanced fertilizer for healthy organic vegetables.
“

We need to teach people that those nutrients are a very valuable commodity and that they can be captured in a simple aquaponic system,” Creaser said. “Aquaponics is the wave of the future.”

Since building his first commercial hydroponic system in 1953, Creaser’s clients have ranged from commercial growers with more than 600 acres of greenhouse facilities to smaller subsistence farms in impoverished nations. Among his most recent clients is Raffles, a new resort in the Grenadines that includes the Trump Island Villas, a Trump-run casino and Trump International Golf Course.

“The system allows them to have fresh fish and vegetables available year-round,” Creaser said. “It’s an extremely expensive resort and their clientele demands absolutely fresh and beautiful produce. If they have to bring their vegetables in, even by air freight, they’re not going to get the same quality they do growing them there.”

While not all of Creaser’s hydroponic clients are set up for aquaculture, the systems that include fish are now set up so that all nutrients are captured. “You can build them to have zero waste, and even go back in and retrofit older aquaculture systems to capture the nutrients.”

In sophisticated systems where optimum growth is important, water is carefully monitored for ammonia, pH and electrical conductivity (EC), but aquaponics is much like gardening, he said. “One of the reasons I’ve been so successful is that we keep it as simple as possible. EC might be perfect at about 2000 but it could go down to 1800 or up to 2500 without really hurting anything.”

“Victory Garden for the New Millennium”
To Geissler, aquaponics is the “victory garden of the new millennium,” providing hundreds of pounds of fish and fresh vegetables for hungry families in poor nations as well as healthy food for families concerned about high levels of pesticides in the foods they purchase.

Geissler has transformed an 11-acre tropical fish farm outside Dade City into an international hub for aquaponics students. They learn how to operate the systems and take that knowledge back to countries like Haiti, Dominican Republic and Guatemala where they work with local groups to create community aquaponics systems.

A member of Rotary International, Geissler helps students raise funds in the U.S. for larger systems. Once they’re back in their own country, local Rotarians provide ongoing support and accountability for operations that provide jobs and food in regions where both are scarce.

Formerly a soldier in the French Foreign Legion, a successful plumbing contractor and an award-winning boat builder, Geissler became a fish farmer after a mission to Guatemala. “I saw poverty and hunger first hand, and God showed me how I could help.” GG

To learn more about aquaponics you can visit these websites:

http://rps.uvi.edu/AES/Aquaculture/aquaponics.html , the University of the Virgin Islands is an international leader in aquaponics and their site features awe-inspiring photos and detailed information on how and why their systems work.

http://attra.ncat.org/attra-pub/aquaponic.html , is written by the National Sustainable Agriculture Information Service, primarily for commercially growers.

www.aquaranch.com helps design and construct aquaculture systems for hobbyists up to large commercial growers.

www.backyardaquaponics.com , lots of photos and an online forum, focus is selling information not systems. _

Vicki Parsons is an environmental writer and a sixth-generation Florida farmer who owns Neem Tree Farms near Tampa.