Published 1:09 pm Wednesday, May 14, 2025
HAGERMAN, Idaho — To Jacob Bledsoe, a University of Idaho aquaculture researcher and extension educator, a rainbow trout’s insides are as important as its colorful exterior.
He and his research teammates identified the genetic markers — DNA sequences with known locations on chromosomes — and the processes associated with rainbow trout being capable of storing high levels of human-healthy omega 3 fatty acids in their fillets while eating a plant-based diet rather than feed derived from ocean sources.
“It gives producers the option to use a different strain of trout that can reduce their input costs while producing a very high-quality fish that might offer even better nutritional resources,” Bledsoe said in a UI news release. The project involves the UI Aquaculture Research Institute and USDA.
South-central Idaho leads the U.S. in production of farm-raised rainbow trout. Trout farms traditionally raised fish on diets heavy in omega 3s from fish meal and fish oil. Feeds based on crop ingredients such as soy protein and canola oil can be produced renewably and at a much lower cost, but most trout are inefficient at producing omega 3s from plant-based feed.
As for marine-based diets, “the problem is that we’ve pretty much maxed out the level of supply the last 10-12 years,” Bledsoe said in an interview. “There is not a lot of supply there to meet the growth of the industry. And you could argue it is a more sustainable production pipeline and you’re not fishing out the oceans.”
Plant-based diets can produce an allergic-like reaction that causes inflammation, he said. The inflammation reduces a trout’s growth rates and increases disease susceptibility.
The researchers for years have been working on the problem through selective breeding, “and in the last few generations, our fish can thrive,” Bledsoe said.
Researchers are in their 12th generation of selection — the work is centered at the Hagerman Fish Culture Experiment Station — and now have “a really successful genetic strain,” he said. Commercial trout farms in the region are incorporating the genetics.
Among other characteristics, this strain of rainbow trout accumulates omega 3s at greater levels on a plant-based diet compared to a marine-based diet.
Traditional genetic selection produced the result and questions remained, Bledsoe said. “We didn’t know the biology or mechanisms that explained how we got to this.”
Researchers used advanced molecular biology tools to characterize genetic and protein expression in the fish, particularly in high performers compared to lower performers, he said. “It came down to a few specific pathways.”
The most important markers the researchers studied are associated with a trout’s level of fatty acid binding proteins, which bind onto lipids and traffic them to the liver, where the proteins can be metabolized efficiently, according to UI.
“We identified specific markers within the lipid pathway that could be important, and fatty acid binding protein was the predominant one,” Bledsoe said in the release. “We were able to show that a fish’s level of fatty acid binding protein correlates tightly with the ability to deposit omega 3s. Generally speaking, there is a lot in the genome that controls the expression of fatty acid binding protein.”
The journal Aquaculture Reports published the team’s findings. The paper’s authors are Ken Overturf and Jason Abernathy of USDA’s Agricultural Research Service; Dietmar Kultz of the University of California, Davis; Bledsoe; Shawn Narum of the Columbia River Intertribal Fish Commission; and Thomas Welker of USDA ARS.
