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To understand global aquaculture — its potential and its problems — it helps to look at the industry's track record in China, a country responsible for 61% of the world's aquaculture. China has begun exporting industrially produced catfish, shrimp and tilapia in recent years. As production pressures have ramped up, Chinese manufacturers have packed their ponds more tightly, leading to disease and pollution from fish waste. That waste can overload coastal waters with nutrients, causing dead zones that can strangle sea life. To fight the diseases worsened by crowding, Chinese fish farmers have liberally used antibiotics and other drugs, including malachite green, an antifungal agent and potential carcinogen that was banned by Beijing in 2002 but shows up periodically in exports. "It is still a problem," says Wong Ming Hung, a biology professor at Hong Kong Baptist University. While China remains a laggard on safety — though experts say its fish-farming industry is improving as it matures — there's no denying that aquaculture can be messy. A badly run near-shore farm of 200,000 salmon can flush nitrogen and phosphorus into the water at levels equal to the sewage from a town of 20,000 people. But for all that, fish farming's bad reputation isn't entirely deserved, especially if it's compared with farming on land. Farmers have had thousands of years to improve agricultural methods and breed domesticated animals like cows and pigs with maximum efficiency. And industrial agriculture can be polluting: the dead zone in the Gulf of Mexico is due largely to fertilizer runoff from the Midwest. Modern aquaculture is just a few decades old, and as producers have become more experienced, they've cut down on pollution and bred more-efficient fish. Many environmental groups that once opposed aquaculture now seek to work with the industry. The World Wildlife Fund (WWF) is leading the way in this effort, helping develop sustainability standards for farmed species. "Our industry is under a lot of scrutiny, and we're doing our best to alleviate those worries," says Nell Halse of Cooke Aquaculture, a major producer in Canada and the U.S.And no matter how much room the industry has for improvement, aquaculture usually puts less stress on the environment and requires less caloric input to yield a pound of protein than meat production. Part of that is simply a result of biomechanics and metabolism. Unlike land animals raised for food, fish are cold-blooded and live in the water, which means less of their feed is wasted — from our point of view — being burned as energy to keep warm or to build bone. Fish farmers had the bad luck to come along after industrial meat production was well established, and the new guy on the block gets more scrutiny. "We have to address the environmental and social issues," says Jose Villalon, director of the WWF's aquaculture program. "But aquaculture is a good tool to deal with food security."

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