This is Steve Ember with the VOA Special English Agriculture Report.

Fish is an important food for many people. In some places, it is the only animal protein to be found. For years, scientists have worried about supplies of ocean fish. As wild catches have decreased, many nations have turned to fish farming.

The United Nations Food and Agriculture Organization says farmed fish represented four percent of world fish production in nineteen-seventy. By two-thousand it was twenty-seven percent.

China is the largest producer of fish, farmed or wild. In two-thousand, China harvested about twenty-five million tons of farmed fish. India, Japan and Thailand are also big producers.

Fish farming has long been considered a way to improve the diets of people in developing areas. The F.A.O. says developing nations produce ninety percent of all farmed fish.

But there are some problems connected with fish farming. Critics say it can cause not just water pollution. They say there is also “genetic pollution” when farmed fish reproduce with wild fish.

Others say that farming some kinds of seafood is wasteful. They argue that salmon and eel, for example, eat more resources than they provide. Often they are fed with products prepared from wild fish.

Also, a recent study of farmed salmon found that their food may contain higher levels of industrial pollution than salmon eat in the wild. But these levels were still well within legal limits.

Another issue involves the lack of international rules about the use of antibiotics in farming. Some farmers feed these drugs to fish, just like cows and other animals, to prevent infections. The F.A.O. notes that there can be health risks to humans who eat the drugs through their food. Experts are concerned that this also reduces the effectiveness of antibiotics.

The farmed fish industry is growing quickly in Asia. It is also growing in other parts of the world, including North America. In the United States, the value of the aquaculture industry has reached one-thousand-million dollars. That is one-third the value of the capture fishing industry.

But scientists say most kinds of wild fish have been harvested too much. Farmed fish can help reduce pressure on populations in the wild. Still, experts and organizations like the F.A.O. warn that just like any other kind of farming, good methods are required.

This VOA Special English Agriculture Report was written by Mario Ritter. This is Steve Ember.