More than 90% of popular freshwater fish in Southern California are carrying human-infecting parasites, researchers say. This poses a significant danger for those who like to eat freshly caught freshwater fish. But there are ways to protect yourself.

The parasites are called trematodes. Two species of the flatworms were discovered in California’s freshwater fish, according to a study published Tuesday in the Journal of Infectious Diseases . The tiny, flattened and sluglike creatures can cause gastrointestinal problems, weight loss and lethargy when a person eats an infected fish.

In some rare and severe cases, the parasites have caused strokes or heart attacks.

“Americans don’t usually think about parasites when they eat freshwater fish because it hasn’t historically been an issue her

See Full Page