As farmed fish industry grows, so does dependence on wild fish

By Beth Daley
Globe Staff

Having fish for dinner tonight? Chances are fifty-fifty it came from a farm.

A new online report in the Proceedings of the National Academy of Sciences notes that aquaculture is expected to hit a landmark by the end of this year - supplying half of the total fish and shellfish people eat in the world.

Salmon being fed at a Maine Fish farm (file photo/AP)

But that growth in aquaculture is placing pressure on wild fish stocks because farmed fish are often fed less expensive wild fishmeal and fish oil to help them grow faster and become more flavorful. While the industry has worked hard to reduce the amount of fishmeal they use per fish, there is so much more farming going on, aquaculture is increasingly taking a larger piece of the fishmeal and fish oil produced around the world.

The international study, led by Rosamond L. Naylor of Stanford University examined aquaculture trends in several species. Vegetarian species, such as Chinese carp and tilapia began being fed more fishmeal in the 1990s to increase yields. That changed between 1995 and 2007 when farmers reduced the share of fishmeal in carp diets by 50 percent and in tilapia diets by nearly two-thirds. Still, in 2007, those fish farms together consumed more than 12 million metric tons of fishmeal.

“Even the small amounts of fishmeal used to raise vegetarian fish add up to a lot on a global scale,’’ said Naylor.

One of aquaculture’s largest consumers of wild fish is salmon farms, where up to five pounds of wild fish is used to produce one pound of salmon. Salmon is one of the most popular farmed fish in the world, in large part because they contain fatty acids that can combat heart disease.

The researchers said a four percent reduction in fish oil fed to salmon would translate into needing only about four pounds – not five – to produce a pound of salmon. The scientists also pointed to other ways to feed fish, such as using protein from grain and extracting fatty acids from single-cell microorganisms and genetically modified land plants.