THE LOKO KUAPA WAS a simple system. Ancient Hawaiians piled lava rocks in shallow seawater to form walled pools. The small fish that swam in at high tide got trapped and grew to harvest in a natural cage kept clean and balanced by the washing waves.

Today?s high-volume industrial fish farming is not so benign. The fish produce a lot of waste that pollutes the surrounding water, and when they escape, they can spread their inferior (or perhaps even genetically engineered) traits into the wild. What?s more, in order to taste good, the farmed fish are fed meal made from large amounts of the wild fish they eat naturally.

But, as Melissa Pasanen writes in The Art of Eating (#61, 2002), environmental designer John Todd and his colleagues at Ocean Arks International (OAI) are working to invent better fish farms far from the ocean. As president of OAI in Burlington, Vermont, Todd leads an effort to devise new ?ecotechnologies? for raising fish, complete with a series of linked, miniature ecosystems for purifying their water and producing some of their food. Often called ?living machines,? Todd?s recent projects include a system for growing a popular African freshwater food fish called tilapia.

In an early step, Todd and his crew mix straw with spent grains from a local brewery to grow organic mushrooms, the first of several crops that can be produced by the process. After the mushrooms are harvested, the remaining material is ready to be used to raise worms for feeding the tilapia.

The tilapia live in a tank whose water circulates through three other tanks, each holding a different but related aquatic community. The tanks nurture plenty of duckweed and algae that the fish will eat along with their worms. This second food source creates a highly efficient system that actually consumes less animal protein than it produces. (Conventional fish farms tend to use far more.) Meanwhile, other rooted plants in the tanks are naturally processing waste from the fish. Compost from the system can also be used to fertilize various crops grown in nearby plots.