By Chris Arsenault
ROME (Thomson Reuters Foundation) - Fish farmers in China have been increasingly harvesting wild stocks in order to feed their caged varieties, putting new strains on the world's oceans, said new research from scientists at Stanford University.
China is the world's largest producer and consumer of fish, contributing about one third of the global supply.
Its production has tripled in the last 20 years, with about 75 percent coming from fish farms, according to the study published this week in the journal Science.
If the industry used more waste from caught fish, along with plant proteins like algae or ethanol yeast to feed farmed fish, then aquaculture could become more sustainable, the study said.
"If the country makes proactive reforms to its aquaculture sector, like using fish-processing wastes instead of wild fish, and generally reducing the amount of fishmeal in aquafeeds, it can greatly improve the sustainability of the industry," Ling Cao, of Stanford's Center on Food Security and the Environment, said in a statement.
"If not, the consequences for the entire global seafood supply chain are going to be really serious."
Globally, fish farming has been growing between 5 and 8 percent annually for the last two decades, said Jogeir Toppe, of the UN's Food and Agriculture Organisation.
He expects the rapid growth to continue as catches of wild fish plateau and demand rises.
"China has been the main driver of this growth," Toppe told the Thomson Reuters Foundation. "This is expected to continue."
The fast growth comes with concerns over environmental sustainability and human health, Toppe said, as farmed fish are often fed large amounts of antibiotics and other chemicals.
Aquaculture companies in China have made some progress in reducing the amount of wild fish fed to captured stock by using waste from other processing plants or algae, the study said.
However, farms often use so-called "trash fish" or less valuable, small breeds caught in the wild to feed bigger, more expensive varieties such as carp or tilapia.
Waste by-products from seafood processing plants is often discarded or dumped into nearby waterways. Some firms refine this waste to use as feed for other fish, but scientists said more must be done to create a sustainable industry.
Officials from the Chinese Academy of Fishery Sciences, a government body, did not immediately respond to requests for comment.
(Reporting By Chris Arsenault; Editing by Ros Russell)