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By Lester R. Brown
Aquacultural output, growing at 11 percent a year over the past decade, is the fastest growing sector of the world food economy. Climbing from 13 million tons of fish produced in 1990 to 31 million tons in 1998, fish farming is poised to overtake cattle ranching as a food source by the end of this decade.
This record aquacultural growth is signaling a basic shift in our diet. Over the last century, the world relied heavily on two natural systems-oceanic fisheries and rangelands-to satisfy a growing demand for animal protein, but that era is ending as both systems are reaching their productive limits. Between 1950 and 1990, beef production, four fifths of it from rangelands, nearly tripled, climbing from 19 million to 53 million tons before plateauing. Meanwhile, the oceanic fish catch grew from 19 million to 86 million tons, more than quadrupling, before leveling off. Since 1990, there has been little growth in either beef production or the oceanic fish catch. Additional production of beef or seafood now depends on placing more cattle in feedlots or more fish in ponds. At this point, the efficiency with which cattle and fish convert grain into protein begins to reshape production trends and thus our diets. Cattle require some 7 kilograms of grain to add 1 kilogram of live weight, whereas fish can add a kilogram of live weight with less than 2 kilograms of grain. Water scarcity is also a matter of concern since it takes 1,000 tons of water to produce 1 ton of grain. But the fish farming advantage in the efficiency of grain conversion translates into a comparable advantage in water efficiency as well, even when the relatively small amount of water for fish ponds is included. In a world of land and water scarcity, the advantage of fish ponds over feedlots in producing low-cost animal protein is clear.
With overfishing now commonplace, developing countries are turning to fish farming to satisfy their growing appetite for seafood largely because the oceanic option is not available to them as it was earlier to industrial countries. For example, as population pressure on the land intensified in Japan over time, it turned to the oceans for its animal protein, using scarce land for rice. Today Japan's 125 million people consume some 10 million tons of seafood each year. If China's 1.25 billion were to eat seafood at the same rate, they would need 100 million tons-the global fish catch. Although at least 220 species of fin fish, shellfish, and crustaceans are farmed commercially, a dozen or so dominate world output. Among the fin fish, five species of carp-all widely grown in China-lead the way with a combined output of some 11 million tons in 1998, more than a third of world aquacultural output. Among shellfish, the Pacific cupped oyster, at 3.4 million tons (including shell), dominates, followed by the Yesso scallop and the blue mussel. In China, fish are produced primarily in ponds, lakes, reservoirs, and rice paddies. Some 5 million hectares of land are devoted exclusively to fish farming, much of it in carp polyculture. In addition, 1.7 million hectares of rice land is used to produce rice and fish together. Over time, China has evolved a fish polyculture using four types of carp that feed at different levels of the food chain. Silver carp and bighead carp are filter feeders, feeding on phytoplankton and zooplankton, respectively. The grass carp, as its name implies, feeds largely on vegetation, while the common carp is a bottom feeder, living on detritus that settles to the bottom. Most of China's aquaculture is integrated with agriculture, enabling farmers to use agricultural wastes, such as pig manure, to fertilize ponds, thus stimulating the growth of plankton. Fish polyculture, which typically boosts the fish yield per hectare over that of monocultures by at least half, also dominates fish farming in India. As land and water become scarce, China's fish farmers are intensifying production by feeding more grain concentrates to raise pond productivity. Between 1990 and 1996, China's farmers raised the annual pond yield per hectare from 2.4 tons of fish to 4.1 tons.
U.S. catfish production is concentrated in four states: Mississippi, Louisiana, Alabama, and Arkansas. Mississippi, with some 174 square miles (45,000 hectares) of catfish ponds and easily 60 percent of U.S. output, is the catfish capital of the world. Among the aquatic species that are widely farmed, two especially wreak extensive environmental havoc-salmon, with production of 700,000 tons per year, and shrimp at 1,100,000 tons per year. Salmon are grown mostly in industrial countries, principally in Norway, for consumption in those countries. Shrimp, by contrast, are grown largely in developing countries, importantly Thailand, Ecuador, and Indonesia, for export to more affluent societies. Salmon, a carnivorous fish, are fed a diet consisting primarily of fishmeal that is typically made from anchovies, herring, or the remnants of fish processing. In stark contrast to the production of herbivorous species, such as carp and catfish, which lighten the pressure on oceanic fisheries, salmon production actually intensifies pressure because it requires up to 5 tons of landed fish for each ton of salmon produced. Another concern is that if farmed salmon, which are bred for fast growth and not for survival in the wild, escape because of damage to the pens by storms or attacks by predators, such as harbor seals, they can breed with wild salmon, weakening the latter's capacity to survive. Fish grown in offshore cages or pens, as salmon frequently are, also concentrate large quantities of waste, which itself presents a management problem. For example, the waste produced by farmed salmon in Norway is roughly equal to the sewage produced by Norway's 4 million people. Shrimp are often produced by clearing coastal mangrove forests which protect coastlines and serve as nurseries for local fish. Mangrove destruction can cause a decline of local fisheries that will actually exceed the gains from shrimp production, leading to a net protein loss. In addition, because shrimp rations are also high in fishmeal, shrimp, like salmon, put additional pressure on oceanic fisheries. A world that is reaching the limits with both oceanic fisheries and rangelands while adding 80 million people each year needs efficient new sources of animal protein. Herbivorous species of fish, such as carp grown in polycultures, carp grown in combination with rice, or catfish grown in ponds, offer a highly efficient way of expanding animal protein supplies in a protein-hungry world. Fish farming is not a solution to the world food problem, but as China has demonstrated, it does offer a potential source of low-cost animal protein for lower income populations. The forces that have made aquaculture the world's fastest growing source of animal protein over the last decade are likely to make it the fastest growing source during this decade as well. |
In the United States, catfish, which require only 1.6 kilograms of feed to gain 1 kilogram of live weight is the leading aquacultural product. With U.S. catfish production last year at roughly 600 million pounds (270,000 tons), or more than 2 pounds for each American, U.S. consumption of catfish exceeded that of lamb and mutton.
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