Commercial fish farms have long been touted as a way to boost the global seafood harvest while taking the pressure off Earth's overtaxed oceans. But it hasn't worked out that way, researchers say.
They conclude that aquaculture -- the production of everything from catfish to shrimp -- has instead raised demand for some ocean fish such as anchovies that are ground into fish meal to fatten their domesticated cousins.
What's more, the researchers say, fish farming has created vast amounts of animal waste that has fouled coastal areas where fish and shellfish are being raised.
In addition, they say, domesticated fish such as salmon have escaped from offshore holding cages where they are grown, displacing their smaller, wild relatives.
''There's a perception that farmed fish completely relieve the pressure on the oceans. But people have completely missed the connection, that it really is very reliant on the oceans and is having a big impact on them,'' said Rosamond L. Naylor, a senior fellow at the Institute for International Studies at Stanford University.
Naylor led a study published in Thursday's issue of the journal Nature. The researchers, from Sweden, Britain and the Philippines, included members of the World Wildlife Fund and the Environmental Defense Fund.
Commercial fish farms produce about one of every three fish humans eat.
Aquaculture experts said the paper raises valid concerns they have been trying to address for years. Still, they said it overlooks research advances and management changes already helping the industry reduce its environmental impact.
''As with any new industry, there are some growing pains, and we believe we're getting on top of those,'' said Chris Kohler, director of the Fisheries and Illinois Aquaculture Center at Southern Illinois University in Carbondale, Ill.
Paul Brown, a professor of aquaculture at Purdue University, said he and other researchers have developed diets without fish meal for rainbow trout and are working on vegetable-based diets for hybrid striped bass and yellow perch.
''If we're going to get to the huge numbers that are expected for aquaculture development, we simply don't have enough fish meal on the planet to do it,'' Brown said.
Other feeds in development could reduce the amount of waste produced by farmed fish, he said.
Over the past 25 years, aquaculture has experienced tremendous growth and, in 1997, nearly 30 million metric tons of fish were produced -- twice the 1990 harvest, said Edwin Rhodes, aquaculture coordinator for the National Marine Fisheries Service.
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