Early Mortality Syndrome, or EMS, results in embryonic mortality in salmon, steelhead trout, brown trout, lake trout, and Chinook salmon. The symptoms of EMS include loss of equilibrium, swimming in a spiral pattern, lethargy, hyper-excitability, hemorrhage and death, which occurs between hatching and first feeding.

“Vitamin B1, or Thiamine, is an essential nutrient that animals must obtain through their diet,” said Chris Ottinger, a USGS immunologist and lead author of the study. “We found that alewives, one of the main diets of many Great Lakes fish, contains an enzyme called “thiaminase” that destroys the thiamine in fish that consume them. The lack of B1 leads to Early Mortality Syndrome as well as the newly reported immune dysfunctions that may be perpetuating infectious diseases in this fish community.”

Alewives came into the Great Lakes when the Welland Canal was built as invasive species. They dominated the prey base until Pacific salmon were introduced in part to control their population levels.