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By Niecole Killawee

As salmon farmers face increased demand because of rising populations around the world, finding a way to use sustainable sources of fish feed in their operations is critical. The aquaculture industry is key to helping society meet global food security needs and that’s why Stefanie Colombo, a Canada Research Chair in Aquaculture Nutrition at Dalhousie University, is focusing on innovative research to help reduce the environmental toll of fish farming.  

Atlantic salmon require a certain amount of omega-3 fatty acids in their diet for optimal growth and health. In the wild, most salmon obtain adequate levels of omega-3 when they eat smaller fatty fish like sardines and anchovies. To round out the dietary needs for farmed salmon, 30-40 per cent of their feed is harvested from those wild fish. The other 60-70 per cent is plant-based feed and doesn’t contain omega-3s. 

“Harvesting these low trophic fish like sardines and anchovies isn’t good because you’re taking a really important piece of the ecosystem,” says Dr. Colombo, an assistant professor in the Faculty of Agriculture’s Department of Animal Science and Aquaculture. “It’s sort of like Jenga. When you take a piece out of the bottom, the whole thing can topple.”

The combination diet is a result of ongoing efforts from the industry to do away with the use unsustainable feeds that rely on limited ocean resources but, so far, the complete elimination of fishmeal and fish oil from feed hasn’t been possible. 

Landlocked salmon strains, however, may hold the key. Dr. Colombo says that these fish have had to adapt to freshwater environments where sources of omega-3s are far less available than they are in the ocean. As a result, it’s suspected that landlocked salmon have the ability to synthesize some of their own omega-3s. That led Dr. Colombo to the conclusion that genetics might unlock a solution to the fish feed problem in aquaculture. 

With that in mind, she looked for support from the OFI seed fund to conduct a proof-of-concept study that took place in 2019. 

“It was the perfect pot of funds to explore that idea, to see if it was commercially viable or not,” says Dr. Colombo. “Based on the results, it definitely seems worth pursuing commercially.”

Dr. Colombo partnered with Dr. Matthew Rise’s team at Memorial University and the United States Department of Agriculture (USDA) to determine if landlocked salmon do indeed have a higher capacity to create their own omega-3s in the absence of dietary sources. That ability would suggest that their genetics could prove useful in the effort to move commercial strains toward a completely plant-based diet someday. In other words, Dr. Colombo was interested in whether or not salmon could become vegetarians. 

The researchers compared two groups, each consisting of a landlocked strain and a commercial strain. One group was fed an experimental fish-free diet while the other was fed the standard diet containing fish oil. The team looked at the genetic expression of each strain under both diet programs and found evidence that landlocked and commercial strains have the ability to synthesize their own fatty acids on a plant-based diet, but the landlocked strain was better at synthesizing omega-3s specifically. 

In addition, the landlocked strain grew 20 per cent more when fed a plant-based diet compared to when fed a fish-oil diet, indicating that lake dwellers may be better equipped to use the more sustainable feed. 

But the commercial strain grew faster regardless of the diet, likely because those salmon have been bred for fast growth since the ‘80s and therefore already have an advantage over the wild, landlocked strain. To preserve that advantage, Dr. Colombo believes landlocked genes should be introduced to the commercial strain through a very targeted approach rather than through crossbreeding.  

“That way we can have the best of both worlds,” she says. “We can still have fast-growing fish, but they can use plant-based diets way better.”

Dr. Colombo’s team is now in the process of publishing their study and plans for a follow-up study that will investigate outcomes in a more domesticated strain of landlocked salmon are in the works. 

Next steps will also include a research collaboration with an industry partner to further explore commercial application opportunities. In addition to addressing ecosystem collapse concerns, vegetarian salmon are cheaper to feed and result in lower production costs for salmon farmers overall. 

“The bottom line is that they’ll have a more robust and efficiently produced salmon product,” says Dr. Colombo. “It could be the next generation of salmon.