Friday February 6, 2026
bioGraphic —
Scientists have conclusively identified the cause of a lethal vitamin deficiency that is driving the demise of one of California’s unique salmon populations. In a recent paper, a team of 37 biologists, physiologists, and fisheries experts show that a severe, widespread vitamin B1 deficiency plaguing the winter run of Sacramento River chinook (Oncorhynchus tshawytscha) is linked to an extreme dietary imbalance caused by the spread of northern anchovy (Engraulis mordax) up the coast.
Historically, some 200,000 winter-run chinook returned each year to spawn in the Sacramento River. Already stressed by rising temperatures in a river divided by dams and overdrawn by farmers, this federally-endangered salmon population has been listed as endangered under the U.S. Endangered Species Act since 1994, and is bolstered by hatchery-raised fish. In early 2020, as the onset of the global COVID-19 pandemic disrupted life on land, managers in salmon hatcheries across California’s Central Valley were faced with the arrival of a different affliction. Hatchery workers were reporting juvenile fish, or fry, swimming in erratic, corkscrew patterns—a characteristic reaction of fish to a vitamin B1 deficiency. They were also suffering a soaring death rate.