Researchers put farmed fish on vegetarian diet
BALTIMORE—Researchers say they may have overcome a roadblock in efforts to satisfy the world's growing demand for seafood through fish-farming.
While more fish are being farmed, taking pressure off wild stocks, environmentalists and fisheries experts are concerned that expanding current fish-farming methods will not be sustainable for many species because that would require more smaller fish to be caught for feed. And that can affect stocks of larger wild fish higher on the food chain.
Researchers at the Institute of Marine and Environmental Technology say they have developed a plant-based diet for three popular saltwater fish -- striped bass, cobia and Mediterranean sea bream. Taste-testers can't tell the difference between fish raised on the plant-based diet and those raised on fish meal, they say.
The two diets both contain fish oil, so neither was totally fish-free, but the researchers also raised fish on a vegetarian diet using wheat, corn, soy and algae meal to replace the oil. That raises the possibility of fish-free aquaculture for saltwater, carnivorous fish, said Aaron Watson, a graduate student at the institute.
"If we want to get aquaculture to expand, we need to find alternatives," Watson said.
Aquaculture for the first time this year accounted for more than half of global seafood consumption and is being looked at to keep up with increasing demand, said Tom Pickerell, senior science manager at Seafood Watch, a program at the Monterey Bay Aquarium that provides evidence-based recommendations on seafood consumption.
"It's really future planning. If we want to double or triple the amount of aquaculture production, we're going to have to look for alternative ways" to feed farmed fish, Pickerell said.
More than a quarter of all fish caught in 2008 were used for nonfood products, mainly fish meal and fish oil for farmed animals, according to the Food and Agriculture Organization of the United Nations.
And much of the fish meal and fish oil currently fed to farmed fish is made from small fish such as menhaden, a filter-feeder that eats algae and plays an important ecological role in the health of waterways such as the Chesapeake Bay. It not only helps clean the water but provides food for larger species. Fisheries regulators voted this year to cut the menhaden harvest on the East Coast by more than a third to protect the population.
Menhaden are also processed into fish oil capsules high in omega-3 fatty acids that are popular among consumers for their health benefits. Watson said the algae meal in the vegetarian diet also provides those healthy oils to fish.
A number of groups worldwide are working on the problem, and algae is one of the main areas being researched as a feed alternative, Pickerell said.
In addition to finding substitute feeds, others are studying so-called polyculture, raising multiple species together to reduce waste and increase production, said Anamarija Frankic, the director of the Green Boston Harbor Project at the University of Massachusetts Boston and a professor of coastal ecosystem management.
While tests show fish raised on the plant and algae diet have the same levels of heart-healthy fats as wild fish, the vegetarian diet also could help in marketing to consumers because the fish are grown in isolated systems and have much lower levels of contaminants such as mercury than wild fish, Watson said.
The algae meal is already used as an additive for feeding brine shrimp and other smaller organisms that are then fed to farmed fish when they are young. The only drawback is the algae meal is a little more expensive, adding about 50 cents a kilogram to the cost of the feed, which cost between $1.40 and $3.20 a kilogram depending on supplier and mix, Watson said.
Fish grown on the fish meal and the plant and fish oil diets were tested at the Center for Food Science and Technology at the University of Maryland-Eastern Shore in Princess Anne, where they were baked and put before panels of tasters.
"The first question we want to answer is whether people can discern the difference, whether it's appearance, odor flavor, texture or mouth feel, and so far it appears they can't," said Thomas Rippen, a UMES seafood technology specialist.
Watson said he is now working on his doctoral dissertation and there are no immediate plans to taste-test fish grown on the totally vegetarian diet. But he hopes that more taste tests will be conducted in the future.