Malawi is a landlocked country in southeastern Africa, primarily known for its tobacco. At least 90 percent of the more than 12 million Malawians are farmers, typically with small spreads of less than one hectare (roughly 2.5 acres). At least one in five adult Malawians are infected with HIV/AIDS, often rendering them incapable of heavy farm work. Researchers discovered, though, that they could boost the farmers' health—and double their income—by simply digging a 200¿square-meter (about 2,000-square-foot) pond on the property and stocking it with fish.

Over the past five years, ecologist Daniel Jamu of the WorldFish Center and his colleagues in Malawi dug such ponds for 1,200 households. By stocking them with tilapias—a native African species that thrives in fish farms—they reduced childhood malnutrition in the region from 45 to 15 percent.

"The project has doubled income of affected households, increased consumption of fresh fish [and] increased production of maize through the production of [a] second, off-season crop," Jamu says. "Integration of aquaculture into agriculture systems aims to use existing on-farm resources such as livestock manure, brans from maize and rice—whether from [one's] own farm or [a] neighbor's farm—to produce fish, while at the same time using water harvested in ponds for irrigation of crops."

In fact, the rain-fed ponds enabled farmers to become 20 percent more productive than their peers during times of drought, thanks to the water retention as well as the nutrients left over at the bottom of the pond. "They do dry up in times of drought, but since drought is more short term," on the order of one or two months, Jamu says, "ponds are able to hold water longer…. Hence, farmers can adapt their production quickly by using the pond water and the water supply systems to grow irrigated maize."

The ponds are also efficient, producing 1,500 kilograms (3,300 pounds) of fish for every hectare of pond on just scraps and, with minimal labor, allowing them to be tended relatively easily by even AIDS-ravaged households (as well as fulfilling the increased nutrition needs of the ill). They permit the growth of high-value but thirsty crops such as bananas and guava, although using less water than other forms of animal husbandry. "A kilogram [(2.2 pounds)] of aquacultured tilapia consumes about 3,000 liters [(793 gallons)] of water versus 70,000 liters for a kilogram of beef or 20,000 liters for a kilogram of coffee," Jamu notes.

The project has proved such a success that it will be expanded in Malawi as well as neighboring Mozambique and Zambia to roughly 26,000 farming households. The cost is small: roughly $200 for a pond that will last roughly 20 years and $100 for labor, Jamu says, and satellite geographic information will help place them where both physical and socioeconomic conditions are best. But one cost is rising due to 300 percent growth in such aquaculture in Malawi: "Fingerlings will cost about $10 but prices are rising fast due to increased demand and a shortage of quality fingerlings," he adds.