From the air, the Pearl River Delta in southern China’s Guangdong province resembles a mass of human cells under a microscope. Hundreds of thousands of tiny rectangular blocks, all of them shades of green, are clustered between cities and waterways. Livestock pens are scattered among the thousands of seafood farms that form the heart of the country’s aquaculture industry, the largest in the world.
Beside one of those fish farms near Zhaoqing, on a muggy day in June, a farmhand wearing a broad-brimmed straw hat hoses down the cement floor of a piggery where white and roan hogs sniff and snort. The dirty water from the pens flows into a metal pipe, which empties directly into a pond shared by dozens of geese. As the yellowish-brown water splashes from the pipe, tilapia flap and jump, hungry for an afternoon feeding.
Chinese agriculture has thrived for thousands of years on this kind of recycling—the nutrients that fatten the pigs and geese also feed the fish. But the introduction of antibiotics into animal feed has transformed ecological efficiency into a threat to global public health.
