INTRO: Fish from the wild are a big part of the diet for other fish that are raised in captivity. As Doug Schneider reports in this week's Arctic Science Journeys Radio, that could cause problems for the ocean.

STORY: A lot of the fish we buy in supermarkets or eat in restaurants comes from fish farms, not from the open ocean. But the species that are raised in farms eat a diet of fish from the wild. That's a cause for concern by some people for the long-term impact of harvesting fish from the sea to feed fish in cages. Pete Granger is an aquaculture expert with the Sea Grant program at the University of Washington. He says salmon aquaculture is an example of modern feeding techniques. The salmon, for example, eat food pellets that are a mixture of vegetable matter and ground-up anchovies and other oily fish harvested from the sea.

GRANGER: "The original intent there was to try to duplicate what the fish would be eating in the wild so that the nutritional content of the fish, the flavor of the fish, could be duplicated in the aquaculture setting. And fish meal and fish oil really have such a high energy and fat level that it's the most high energy diet that you can feed to these fish."

Pete Granger says a high-energy diet is important for getting the farm-raised fish to grow quickly so they can be sent off to market. Granger says the fish used in this feed are typically oily ones that people don't like to eat. But he says these wild fish still have a place in the marine ecosystem, and people are aware that overexploiting them could cause problems. For that reason, aquaculture experts are developing fish food that relies more on vegetables and less on fish meal and fish oil. But Granger says major changes will be slow in coming.

GRANGER: "For the foreseeable future, I don't think we can make the switch totally away from fish meal and fish oil. I think you can continue to add grains and vegetable oils, but I don't think you can totally substitute at this point."

This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program at the University of Alaska Fairbanks School of Fisheries and Ocean Sciences. I'm Doug Schneider.

Thanks to Earthwatch Radio for help preparing this script.

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Related reading

News release "New breakthrough in sustainable fish farming" from the Centre for Environment, Fisheries and Aquaculture Science

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