The Promises and Pitfalls of Fish Farming
A generation ago, agriculture responded to the challenge of rising population by achieving big increases in crop yields - but at considerable cost to environmental and social stability. Now, as agricultural productivity flattens while demand continues to rise, high-tech fish farmers are wading into the breach. But can they replicate the successes of the Green Revolution without repeating and compounding its disasters?
The town of Turners Falls, Massachusetts, on the Connecticut River about 150 miles west of Boston, was one of the many small New England towns that thrived during the Industrial Revolution at the turn of the twentieth century. The textile factories and pulp mills of that are long gone, but today the town is part of another development that could have global reverberations. This time, it is part of what might someday be called, an integrated industrial revolution. One of its newer businesses, housed in a corrugated steel building not far from the river, produces fish. Aquafutures, as the name implies, is not a traditional New England fishing enterprise of the kind that launched its boats from the Massachusetts or Rhode Island coast during the country's early history. Through the use of water recirculation technology, the company - one of many in its fast-growing business - is helping to radically change the way fish are produced, and ultimately to determine what role aquaculture will play in supplying food to the world.
Inside this one-acre facility, amidst fish tanks, processing facilities, and support systems, Aquafutures' employees raise hybrid striped bass - a cross between white and striped bass. Shipped in as fingerlings that weigh 2 grams, the bass are kept in this secure environment for about 10 months during which they are given high-protein feeds. Once they reach market-size of about 800 grams, they are shipped to restaurants and supermarkets While this facility may seem far removed from nature, it is in fact fairly well designed to mesh with the resource constraints of natural systems.
By using state-of-the-art recirculating technology, with computers monitoring temperature, oxygen, and chemical levels, the plant can recirculate each liter of water 250 times before it is discharged. Although the process is energy-intensive, the electrical costs are to some degree offset by the gains in water efficiency. High water demand is a major problem for food production worldwide, whether in irrigating agricultural land or in providing future habitat for fish. Aquafutures has minimized not only its water use but its pollution, replicating the waste management practices of local dairy farmers who storehouse manure. Workers periodically scoop out waste from the fish tanks and sell it as a nutrient-rich manure to local corn and vegetable farmers.
A world away, on Phuket Island in southern Thailand, aquaculture is having a very different impact. Not far from four-star resort hotels, shrimp-breeding ponds have blanketed the landscape. In the village of Ao Goong (meaning Bay of Prawns), the rural quiet has been displaced by a constant drone of generators circulating air into the ponds and pumping out wastes.
Unlike their contemporaries in Turners Falls, the people of Ao Goong have not welcomed this new business. The wastes from the ponds have been simply dumped on the ground, causing the villagers' coconut trees to turn brown and their well water to go bad. They can no longer use the wells, and have had to haul in drinking water from somewhere else. When the wastes from the cultivated shrimp were redirected into the bay, wild shrimp were killed - destroying the traditional local economy. For generations, the villagers have made their living by fishing shrimp from the sea, but the arrival of commercial prawn farmers is putting them out of business.
As the people of Phuket Island have learned, the environmental and social costs of shrimp farming can be enormous. Shrimp is the most valuable commodity being produced by the booming aquaculture industry, and arguably the most destructive. But it is not alone: a wide range of indiscriminate and poorly planned fish farming operations are leaving their heavy footprints - destabilizing coastal ecology, degrading farmland, and polluting drinking water supplies.
The conundrum is that fish-farming, if properly done, offers great advantages in resource-use efficiency over both traditional fishing and conventional agriculture - advantages the world can ill afford to squander in an era of impending food scarcity. Indeed, integrated fish and rice farming has formed the backbone of traditional agriculture in Asia for centuries. As the world's expanding human population drives up global demand for new food supplies, the great potential of aquaculture, combined with some of the horrendous ecological and human impacts it has had so far, have created seemingly intractable tensions between its promoters and its critics. How that tension is resolved will go a long way toward determining how - or with what limitations - we will be able to eat in the future.
The Blue Revolution
As far as is known, the earliest fish farming (or aquaculture) took place in China, where the common carp has been a staple food for millennia. A document called "Fish Culture Classic," written by Fan Li nearly 25 centuries ago (in 460 B.C.), details numerous experiments on the sizes of fish ponds, stocking rates, and harvest yields. In rural inland areas, often on marginal lands, small carp ponds supplemented the output from farm crops for centuries; the ponds were supplied with nutrients from an adjoining pig pen, or from other animals, ducks, food preparation, or nightsoil. Several times a year, the ponds were cleaned out and the resulting rich bottom soil was applied to neighboring fields.
When Emperor Lee came to power during the Tang Dynasty (618-917 A.D.), growers shifted from cultivating carp to other types of fish. The shift was an accident of history: the word for carp sounds like the Emperor's name "Lee" in Chinese, and farmers were apprehensive about the connotations of any talk about "eating carp." Other species were put in the ponds. And, because supplies of newly hatched fish varied from season to season, farmers had to make do with whatever they could get, sometimes raising different species together in the same pond. Gradually, a stable and highly productive system of polyculture - raising many fish together - evolved.
Chinese pond-culture systems continue to be among the most productive freshwater fisheries in the world today. One of the keys to their continued success is that nearly all the wastes are put to productive use, so the systems are largely self-sufficient and closed: the waste of one species becomes food for another. In more open systems, unused nutrients attract infestations of bacteria, insects, birds, and other organisms, which upset the balance and deplete the food supply needed by the fish.
In the polyculture pond, available nutrients are matched closely to the feeding habits of various fish. Silver carp and tilapia feed on phytoplankton (microscopic plants), while bighead carp graze on zooplankton (microscopic animals). Grass carp, wuchang fish, and common carp eat green fodder, while common carp, black carp, and mud carp forage in sediments at the bottom of the pond. Species are thus combined to maximize yields and minimize inputs, providing a valuable source of food and protein for local consumption. In a pond about two meters deep, for example, an experienced farmer may raise up to 10 tons of fish per hectare each year.
This sort of small-scale aquaculture has also been long practiced by rural villages in Indonesia and India, using local fish varieties. During the early twentieth century, Chinese immigrants brought their experience with polyculture to Thailand. From there, small-scale "integrated" fish farming - that which efficiently combined the feeding of fish with the raising of plants - spread throughout Southeast Asia. But it was not until well past mid-century that commercial aquaculture began its boom in earnest.
During the late 1960s and 1970s, fish farming was touted by international development agencies as a new source of protein that would sidestep the problems of traditional agriculture - which was facing a gamut of problems with soil erosion, increasing fertilizer needs, and scarcity of fertile land and irrigation water. Fish farming was viewed as a simple yet elegant means of providing food security for growing populations in developing countries. Simply by flooding marginal lands and releasing easy-to-grow fish that most people could afford to buy, social planners predicted, farmers in those countries could create a global revolution in food production.
Indeed, in many ways, aquaculture is a more reliable source of protein than either traditional fishing or farming. Compared to ocean fishing, which can be disrupted when storms or territorial disputes turn boats back, fish farming is less...