Ferry, a lanky redhead in his mid-30's who is the greenhouse's manager, estimates that at Cabbage Hill a pound of fish food is converted into a quarter pound of fish and eight to ten pounds of produce, a veritable cornucopia of chard, bok choy, lettuce, mesclun, beet greens, kohlrabi, tatsoi, basil, parsley, cilantro, tomatoes, sorrel, and rosemary. The tilapia, his largest fish "crop" by total weight, feed on a 100-percent vegetarian diet, getting around a major environmental hurdle faced by farmers who raise carnivorous fish such as salmon, which eat meal made from herring, sardines, and anchovies, which are currently fished to their limit. Typically, several pounds of small fish are needed to produce one pound of salable flesh.
In the half-dozen tanks resembling backyard wading pools that lined one wall of Ferry's operation, thousands of tilapia and striped bass swam in circles, sporadically flipping into the air as if to show off their tastiness. The fish ranged in size from no bigger than my little fingernail to glistening, full-bellied specimens that would stretch across a dinner plate. The water, which would otherwise accumulate toxic levels of fish waste, was pumped continuously out into long, shallow troughs along the opposite wall. There, vegetables grew on polystyrene rafts, their roots dangling into the water, absorbing nitrites and phosphorous, purifying it before it was recirculated to the fish.
Aside from food for the fish, the operation is almost totally self-contained. A small amount of solid waste from the fish is filtered out and composted for application to raised-bed gardens outside the greenhouse. Ferry has to add an occasional scoop of lime to buffer acidity, much as a terrestrial gardener sweetens his soil. The greenhouse's resident population of ladybugs, midges, and parasitic wasps preys on plant-eating insects, eliminating the need for chemical pesticides.
Ferry and his crew harvest vegetables twice a week, 52 weeks a year, selling them to six nearby restaurants and a grocery store and through a farmers' market. The tilapia are purchased live by Asian markets in New York. The bass go to the local restaurants. In all, he sells between 6,000 and 8,000 pounds of fish a year.
The greenhouse runs as project of Cabbage Hill Farm Foundation, an organization dedicated to sustainable agriculture and preserving historic farm animals that was created by the private equity investor Jerome Kohlberg and his wife, Nancy. Because of steep initial investment and the need for almost constant, labor-intensive management, Ferry's aquaponics system is not yet profitable, but it has clearly demonstrated that aquaculture need not be the environmental disaster it too often is. Ferry's enclosed system pollutes no bodies of water. His fish can't escape into the wild and don't spread disease to native species. And they effectively convert a largely vegetarian diet into flesh and vegetables.