BATON ROUGE, La. -- What do you get when you cross a fish with a plant? If done properly, an excellent educational tool and a futuristic food production system.

Aquaponics is a system that combines aquaculture with hydroponics into an efficient, environmentally friendly process.

"The fish waste provides nutrients for the plants, and the plant roots in turn act as a filter to clean the water for the fish," explains George Wardlow, professor of agricultural and Extension education at the University of Arkansas. "It's basically the same kind of system as is found in nature."

The Agriscience Project, co-directed by Wardlow and Don Johnson, professor of agricultural and Extension education, built and distributed dozens of small-scale aquaponics units to junior high and high schools across Arkansas.

An aquaponics unit has three primary components: a fish tank, a filter/oxygen stack for breaking down the fish waste into a usable form for the plants, and a hydroponics apparatus, which is basically a series of pipes or trays with holes in them to physically support the plants. Each hole holds an individual plant and nutrient-enriched water is run through the pipes to continuously feed the plants.

Depending on the system used, the roots may grow directly in water, or the trays may be filled with some type of medium, such as sand, rockwool, or rice hulls.

In standard hydroponics, a supplemental fertilizer would be added to the water, but in aquaponics, water from the fish tank provides the nutrients.

"This kind of system allows us, to some extent, to replace traditional fertilizers in hydroponics systems," says associate professor Mike Evans of the department of horticulture, who has done research in the field of hydroponics.

The water is pumped from the tank into the filter/oxygen stack where bacteria break down the fish waste from ammonium into nitrates, a more usable form of nitrogen. These bacteria must initially be added into the system.

"Special bacterial inoculation kits can be bought to supply the bacteria for the process," Wardlow says. "But what we have found works well is to simply use pond water. It's obviously less expensive than the kits, and already contains the necessary bacteria."

From the filter, the water flows through the hydroponics system, where the plant roots absorb the nutrients and act as a secondary filter, cleaning the water and trapping any unprocessed waste particles before the water returns to the tank where the cycle begins again. With the exception of fish food, which must be added, this system is basically self-sustaining.

For teachers or others interested in constructing their own units, Wardlow says, the department also offers detailed construction plans on its Web site at www.uark.edu/depts/aeedhp/agscience/aquart.pdf.

"These aquaponics units make excellent classroom teaching tools," Wardlow says. "They provide students with "hands on" lessons in applied math, chemistry, physics and biological sciences."

In addition to the educational value, some predict that, with the growing world population and declining farmland, farming techniques like aquaponics might have commercial potential. Already, there are several successful commercial aquaponics farms in existence throughout the world.

Bioshelters, Inc., a commercial aquaponics operation based in Amherst, Mass., produces 30,000 pounds of tilapia fish and 4,000 cases of organic produce annually. In Australia, Tailor Made Fish Farms operates a 42-acre facility near Sydney that grows Australian barramundi fish along with some 240,000 heads of lettuce per year.

P.J. Hirschey, University of Arkansas Department of Horticulture, phirsch@uark.edu