Growing fish in fields.

• Author: Kane, Hal
• Position: Aquaculture parallel to agriculture

As the world's food production falls behind population growth, commercial fish farming is taking up some of the slack. A more efficient producer of protein than beef or poultry, it offers considerable promise. But like farming, it has environmental costs.

Pre-Columbian American farmers once dug moats around their fields. They were not protecting their crops from raiders or thieves, though. They were adding another dimension to agriculture: fish production.

As fertilizers and crop residues ran off the land into the water, they fed the food chain that supported the fish growing there. And from time to time, the farmers took up the silt from the bottoms of the canals and put it onto the fields, turning the fish wastes back into fertilizer.

Anthropologists have not been able to learn why that practice ended in the Americas, though it ended before the coming of the Europeans. But the pre-Columbians were fore-shadowing a development that is now changing patterns of food production worldwide.

Around the world, from Vietnam to Bangladesh, simple ponds have been successfully fertilized by an adjoining pig pen, or by the waste from ducks, kitchen trash, gardens, or nightsoil. Those wastes provide nutrients for the organisms that feed the fish. Periodically, the ponds have been emptied and sterilized by leaves that disinfect, such as tea leaves in China, and then restocked. Production in these rural ponds has been low and inefficient by industrial standards, but farmers have been able to supplement both their diets and their incomes at relatively little cost.

Since the middle of this century, however, that practice has been changing. And while such traditional small-scale aquaculture continues quietly today, fish farming has now entered an era of large-scale, mechanized growth that is significantly affecting the world food economy.

The Limited Wild Catch

The demand for cultivated fish is a spillover from the rising demand for wild ocean fish, which is becoming more and more difficult to catch. Today, foreign fishing vessels are prohibited or regulated within 200-mile "exclusive economic zones" off the coast of almost every fishing nation, reversing the long-standing tenet of "freedom of the seas." From Namibia to Canada, foreign ships have been declared "fish pirates" and turned away.

Governments are also tightening regulations on their own fishers. From reduced quotas in Argentina or the Philippines to outright prohibitions like Canada's ban on cod fishing in the north Atlantic, the new restrictions have become omnipresent. Fishers are now told precisely how much they can catch, when they can catch it, and what equipment they can use. For example, off the coast of California, large "factory" boats are allotted a certain tonnage of catch, and smaller commercial or hobby boats are allotted a similarly limited catch, divided by type of fish and by type of equipment used.

The reason, it turns out, is that the productive capacity of almost every sea has been reached or passed, and almost all catches today come at the expense of other fishers or of future stocks. The Food and Agriculture Organization of the United Nations, the primary world body monitoring fish stocks, says that "global fish production from most marine resources and many inland waters has reached or exceeded the level of maximum sustainable yield." That means that virtually all future growth in fish supplies must come from fish farming.

Massive aquaculture is new enough that careful global statistics were first tallied for the year 1984, by which time more than 6.5 million toils were already hitting the global marketplace, not counting seaweeds or plants. By 1991, world aquaculture had doubled, reaching 13 million tons. That's more than 13 percent of the total world catch, and far more than enough to supply North America at its current consumption levels. About two-thirds of the production comes from inland fish culture - in rivers, lakes, ponds, and buildings. The rest is coastal - grown in bays or in the open ocean. Seventy percent is finfish, such as salmon, flounder, or tilapia. About 24 percent is mollusks, such as oysters and clams, and about 6 percent is shrimp and other crustaceans.

To raise that much fish, the new fish farmers have abandoned the age-old techniques of the ancient Chinese, American Indians, and others. They have expanded their fish production by taking on industrial methods that often bear resemblance to those of modern agriculture - emphasizing the cultivation of a single species raised with the help of large equipment, chemicals, and careful breeding. Where aquaculture had been a balanced complement to agriculture, it has often become a new form of monoculture.

With heavy investments in capital, warehouses have been built to house large tanks. Test tubes have been used to fertilize eggs for hatcheries. In bays and oceans, large areas have been fenced off for fish cages. Fields that were previously planted in corn or wheat have been surrounded by banks and stocked with fish. Fish farming has become a major industry in its own right.

In recent years, fishers who found their mild stocks over-harvested and increasingly restricted have seen that the investments they made in boats could be shifted instead to fish farming. One Irish marine husbandry advocate, angry at restrictions on open-water harvesting of wild stocks imposed by the European Community's secretariat in Brussels, noted that "as yet Brussels has not decided to dictate to us who can and cannot fish farm in our waters."

Following that fellow's logic, many countries have boosted their farming of fish. Between 1984 and 1990, some countries doubled their output: Finland from 9,000 to more than 18,000 metric tons; Denmark from 24,000 to...