In an effort to make fish farming more sustainable, the aquaculture industry has been cutting back on feed made of other fish and replacing it with plant-based alternatives. But a new study warns that may make the fish less healthy to eat and have negative impacts on the environment.
'Those ingredients then have to come from somewhere and as it gets to a larger and larger scale, then that environmental footprint gets quite large.' - Jillian Fry, Johns Hopkins University
Many fish species that are farmed, including Atlantic salmon, the most farmed fish in Canada, are carnivores that eat feed traditionally based on fish meal and fish oil. Environmental advocates such as Greenpeace have criticized the practice as unsustainable, as wild fish that could be used to feed people or maintain wild populations need to be caught in order to produce the fish food.
"They realized that we're grinding up a lot of fish to feed the fish," said Jillian Fry, director of the Public Health and Sustainable Aquaculture Project at Johns Hopkins University in Baltimore, Md.
The price of fish meal and fish oil has also increased with demand.
Canola, soy, corn
Together, that has led to a shift toward plant-based ingredients in fish feed, such as canola, soy, corn, nuts and wheat, Fry and her collaborators note in a new study. Fish meal made up 24 per cent of fish feed in 2000. It was down to 16 per cent in 2008, and is expected to make up just seven per cent of fish feed in 2020.
That's generally seen as a good thing by both scientists and environmental advocates.
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Crop-based replacements are "just seen as widely available and sustainable," Fry said. "What is missing is the fact that those ingredients then have to come from somewhere and as it gets to a larger and larger scale, then that environmental footprint gets quite large."
Fry, along with colleagues at Johns Hopkins and Graham MacDonald at McGill University, combined the information found in many different scientific studies to get a detailed look at the expected environmental and health impacts of using more crops to feed farmed fish. They published their results in the journal Environment International.
"Aquaculture's environmental footprint may now include nutrient and pesticide runoff from industrial crop production, and depending on where and how feed crops are produced, could be indirectly linked to associated negative health outcomes," the researchers wrote.
In addition, they said, the use of plant-based ingredients could reduce the amount of healthy omega-3 fatty acids in fish – one of the things that makes fish like salmon attractive and tasty to consumers.
While this is something salmon farmers are aware of and trying to avoid, Fry says. Omnivorous fish that already eat more plant material and have less omega-3s, such as tilapia, may end up with even lower levels.
"Anywhere it's decreasing in our diet, we need to pay attention."
The study notes that right now, only four per cent of feed crops are used to produce fish.
"But that proportion is going to be steadily increasing because aquaculture is the fastest-growing form of animal production," Fry said. At the same time, other types of animal production are also growing, increasing the pressure on crop production and the environment.
She wants the aquaculture industry to start paying attention to the types of crops that go into the feed, and their environmental footprint.
Meanwhile, she advises consumers to eat a variety of seafood and demand fish that are sustainabley fished or farmed.
Cyr Couturier, research scientist and chair of aquaculture programs at Memorial University in St. John's, says he thinks, in Canada at least, the aquaculture industry is already well aware of the potential health and environmental consequences of moving to more crop-based feeds.
Canada's Atlantic salmon farmers still don't use much plant material in their feed, just a small amount of canola and soy, he said. Instead, they've moved towards replacing fish with fishery byproducts such as fish offal and "frames" — the bones and small amount of flesh left behind when a fish is processed into fillets.
Plankton, bacteria, insects
At the same time, new omega-3-rich alternatives such as plankton grown in land-based tanks, methane-munching bacteria, and insects grown from marine-based feed, are becoming more available.
"It's not going to be a problem to find substitutes for some of the grains," he said.
Even if crops fed to fish have a negative environmental impact, he added, that is still smaller than the impact of growing crops to feed other, less efficient livestock like pigs and cattle.
"Thus, one could easily argue that using crop-based diets for any of the animal proteins consumed by humans (with the exception of insects) should favour the aquaculture species first."
John Werring, science and policy adviser at the David Suzuki Foundation, said he thinks the study's conclusions about the indirect negative consequences of plant-based feed in aquaculture are valid. He suggests that one way to improve sustainability would be to diversify the type of species that are farmed.
"It gives people more choice," he said, "and there are different means and mechanisms that you can use to grow different species."