糖心视频

A pair of Idaho State University researchers are part of a group of more than 30 scientists who've found the culprit responsible for the death of newly hatched fish in an endangered salmon run. The perp: anchovy.

The group's findings, in the Proceedings of the National Academy of Sciences, detail how a lack of thiamine鈥攂etter known as Vitamin B1鈥攍ed to the deaths of up to 50% of newly hatched Sacramento River winter-run Chinook salmon back in 2020 and 2021.

The scientists found that the diet of the endangered fish was being dominated by northern anchovy. The anchovy is in the middle of a population boom, and its territory is expanding into regions of the Pacific Ocean where these Chinook salmon feed.

While abundant, the anchovy packs a one-two punch in terms of depriving the salmon of the critical vitamin. First, the fish is naturally low in levels of B1. Second, the anchovy carries an enzyme that breaks down B1 in the salmon's gut, making it so the salmon do not ingest the vitamin.

"Compared to other main dietary items, anchovy are the worst food for salmon to eat in terms of B1," said Bruce Finney, professor in the departments of biological sciences and geosciences at ISU and co-author of the paper. "B1 deficiency can be so severe that it can cause death early on, but can also affect neurological functions like swimming, making it harder for them to avoid predators and catch prey."

Researchers with the National Oceanic and Atmospheric Administration and other institutions when they saw the young fish鈥攃alled fry鈥攕wimming in either corkscrew patterns or upside down. The scientists were also alerted to instances of salmon species acting similarly in the Great Lakes and as far away as the Baltic Sea in northern Europe.

In both cases, the fish were found to have diets short on B1. Coupled with reports from fishermen of salmon stomachs stuffed with anchovy, researchers thought they might have the offender pegged.

"This mystery has been especially difficult to solve because the source of the problem is in the ocean, but the effects show up in rivers and hatcheries," said Rachel Johnson, a research fish biologist at NOAA Fisheries' Southwest Fisheries Science Center, in a news release.

To confirm, NOAA Fisheries brought together experts from around the nation. That's where Finney and his graduate student, Haskell Distajo, stepped in. In the Stable Isotope Laboratory on ISU's Pocatello campus, they analyzed salmon eggs, looking at the isotope signatures of nitrogen and carbon.

"The unique mix of nitrogen and carbon isotopes found in the eggs lets us know about the diet of the salmon that is passed along to the offspring," explained Finney.

From there, the amount of B1 in the eggs was measured at another lab, and taken together, they could point the finger directly at the anchovy.

"We found evidence that fish that ate a lot of anchovy had low thiamine, and that fish with a different and more diverse diet had higher thiamine," Finney said.

"It is concerning how Chinook salmon are experiencing early death as a result of being unable to control their movement and feed for themselves due to a lack of this vitamin," said Distajo, a master's student studying biology and co-author on the paper. "I am grateful to be able to contribute to finding part of the cause of this dilemma."

B1 deficiencies haven't been documented in Idaho's salmon runs at this time. Like other salmon, though, these fish hatch inland and start their lives in the rivers of the Gem State, make their way to the Pacific, and then return to where they hatched years later to spawn and start the cycle anew. However, it has been found in populations of Alaska salmon and may be more far-reaching than previously thought.

"While Idaho salmon roam in parts of the ocean where anchovy are rare, other salmon prey may also have negative impacts in terms of B1," said Finney. "The ocean is changing pretty rapidly, and this is a fairly understudied aspect of all the stressors potentially influencing salmon."