Sushi Worm surge in Salmon reflects conservation success, study finds

A surprising study shows that the number of parasitic worms in canned salmon has increased over the past four decades, but researchers say it’s largely harmless for most people and actually signals a conservation success story.

Researchers at the University of Washington analyzed cans of Alaskan salmon dating back to the 1970s, finding that parasites, which use salmon as hosts, have become more abundant over time in chum and pink salmon. 

Sockeye and coho salmon, however, showed stable parasite levels.

Chelsea Wood, senior author of the study published in the April 2024 issue of Ecology and Evolution, told People, “We suspect that this is actually a ‘good news’ story. The final hosts of these worms are marine mammals, and their populations have rebounded since the U.S. passed the Marine Mammal Protection Act in the 1970s.”

The worms, often referred to as “sushi worms,” are killed during the commercial canning process, meaning they pose virtually no risk when consuming canned salmon. 

“For the vast majority of us, we can eat live worms with no ill effects—as gross as that sounds, it happens every day,” Wood explained. 

She notes that only individuals allergic to the proteins in the worms may have reactions, even if the parasites are dead.

Consuming raw fish, such as sushi or sashimi, carries more risk, as live worms can penetrate the intestinal wall, potentially causing nausea, vomiting, or, in rare cases, hospitalization. Freezing or cooking fish effectively kills the parasites.

Wood adds, “I eat sushi regularly. We take risks in many aspects of life, and for me, sushi is worth that little bit of risk.”

The study underscores how human food research can reveal unexpected insights about ecosystems, showing how a rise in tiny parasites reflects thriving marine mammal populations and a rare silver lining in our canned salmon.