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Salmon go on veggie diet
MEGAN OGILVIE
SPECIAL TO THE STAR
A browse through the seafood section of your local grocery store may soon reveal a new dinner choice: vegetarian salmon.
A team of Canadian scientists have found that farm-raised salmon can be fed a diet high in vegetable oil without suffering any ill effects. This is good news for fish farmers since it will cost less to feed their stocks. But the consumer may reap the biggest benefit because the fish will have lower levels of contaminants.
The results, presented last week at the Society for Experimental Biology Annual Meeting in Canterbury, England, were met with excitement by people in the aquaculture industry, says Colin Brauner, one of the lead authors of the study and a professor of zoology at the University of British Columbia.
"There is some concern that farmed fish have high levels of some contaminants," says Brauner.
Farm-raised salmon are currently fed pellets made primarily of fishmeal and oil derived from processing wild marine fish such as anchovies, which can be tainted with contaminants, including PCBs and dioxins.
Scientists are eager to find out whether farm-raised fish will thrive on alternative diets that are lower in fishmeal and fish oil and higher in vegetable oils, says Brauner.
The Canadian research may help answer that question. The study found that up to 75 per cent of the dietary fat in a farm-raised salmon's diet can come from canola oil — the other 25 per cent comes from fishmeal or fish oil — without the fish suffering any negative health effects. The seven-month feeding trial on more than 7,000 spring Chinook salmon investigated four different diets, with the canola oil diet providing optimal results.
"As long as we meet the omega-3 fatty acid requirements of the fish with some residual fish oil in the diet, the fish can be successfully reared (on this alternative diet)," says study author Dave Higgs, head of the fish nutrition program at the DFO/UBC Centre for Aquaculture and Environmental Research in West Vancouver. "This is one of the highest replacement levels in marine studies. It looks very promising."
Fish farmers are interested in the study results for a variety of reasons. Fish oil is a finite resource; only so much fish can be caught each year, about a third of which is turned into fishmeal and fish oil, says Higgs. As the aquaculture industry has grown, demand for fish feed has increased dramatically. If the current trend continues, explains Higgs, the total global fish catch could be used for fish feed by 2010.
"Demand will drive up the cost of fish oil and we have to find suitable alternatives that are lower in cost," he says. "Since canola oil is a dominant oil seed in Canada, it's considered to be a very good choice for an alternative fish food."
Fish farmers also want consumers to continue eating farm-raised salmon, says Brad Hicks, vice-president of Paplow Feeds, a major producer of fish feed in Vancouver.
A host of studies released in the past few years has brought farm-raised salmon under scrutiny. A 2004 study published in the journal Science found that farm-raised salmon contained significantly higher concentrations of contaminants than wild salmon. The fish industry — and many health agencies, including Health Canada — responded to the study by telling consumers the health benefits of eating salmon outweighed the health risks from contaminants. Fatty fish like salmon are rich in healthy omega-3 fatty acids which scientists say are good for heart health.
A Health Canada study concluded that levels of contaminants, primarily PCBs, found in both farm-raised and wild salmon were well below their current guidelines of 2 parts per million. Health Canada currently states that eating farm-raised salmon does not pose a health risk to consumers.
Still, fish farmers should be doing more to reduce contaminant levels in farm-raised fish, including salmon, says David Carpenter, author of the 2004 study published in Science and director of the Institute for Health and the Environment at the University of Albany.
His work showed that farmed salmon were more contaminated with PCBS and dioxins than wild salmon, and that the levels of contamination varied depending on where the fish used in the feed were caught.
"If you feed nothing but fish oil to fish being farmed in a cage, you are almost eating hazardous waste," Carpenter says.
Raising farmed salmon on a feed made primarily of vegetable oil is what he recommended in his studies on farm-raised salmon. But researchers needed to prove that farm-raised salmon fed vegetable oil would do as well as salmon fed fishmeal and oil — and that vegetarian salmon would keep the beneficial levels of omega-3 fatty acids that are lauded in the health community.
Last year Scottish researchers reported that rearing salmon on vegetable oil feed up until the final stages before harvesting resulted in salmon with lower levels of contaminants that still had high levels of omega-3 fatty acids.
"Between the Canadian study and the Scottish study, it shows we can reduce levels of contaminants in fish without sacrificing omega-3s," says Carpenter.
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