July 1, 2025 –A vitamin deficiency linked to an enzyme found in anchovies that breaks down Vitamin B1, or thiamine, is threatening the survival of Chinook salmon in California and far beyond.
“An interesting piece of the puzzle is that we don’t have evidence for diminished sources of thiamine in the ocean food web,” said Nathan Mantua, a research scientist with NOAA Fisheries’ Southwest Fisheries Science Center in Santa Cruz, Calif. “Instead, we have evidence that anchovy carry an enzyme called thiaminase that destroys thiamine in the predator’s stomach when the anchovy is digested.”
Mantua is part of the team of 37 coauthors of a new research paper published in Proceedings of the National Academy of Sciences of the United States of America that links Vitamin B1 deficiency to the anchovy-dominated diet that likely resulted in the death of nearly half of California’s wild winter-run Central Valley Chinook salmon fry in 2020-2021.
“It has been a fascinating five years of research working with an entirely new group of people for me in our ongoing investigations into thiamine deficiency in California’s salmon,” said Mantua.
The issue came to their attention just before the Covid-19 pandemic hit the U.S. in January of 2020, so they had to develop a research program at a time when there were lots of big changes happening to the way they worked in the office, on the ocean, and in rivers. In spite of all those hurdles, the group came together to rapidly develop a research network that worked together really well, he said.
A research summary released by NOAA Fisheries on June 25 notes that thiamine deficiency is linked to large-scale shifts in the ocean ecosystem, shifts that changed the prey adult salmon consume before returning to West Coast rivers to spawn. Longtime loss of habitat and water has already weakened many California salmon populations, and further declines from thiamine deficiency or other impacts may lead to their extinction, the report said.