A vitamin deficiency likely killed as many as half of newly hatched fry of endangered winter-run Chinook salmon in the Sacramento River in 2020 and 2021. These new findings were published in the Proceedings of the National Academy of Sciences. The deficiency of thiamine, or Vitamin B1, is linked to large-scale shifts in the ocean ecosystem. These shifts changed the prey adult salmon consume before they return to West Coast rivers to spawn, scientists reported. They said the longtime loss of habitat and water has already weakened many California salmon populations. Further declines from thiamine deficiency or other impacts may lead to their extinction. The deficiency syndrome can also affect salmon runs like the Central Valley’s fall-run that once supported valuable commercial fisheries across California. They have since dwindled to the point that commercial ocean salmon fishing in California has been closed for the last 3 years. … Anchovy manufacture an enzyme called thiaminase that breaks down thiamine and can, in turn, affect salmon that eat large amounts of the small fish.