Love ceviche, sashimi, or a fresh catch from your local lake? A new study has a chilling warning: eating raw freshwater fish could expose you to microscopic parasitic worms, and they’re far more common than anyone realized.
Researchers from the University of California, San Diego, found that 93% of freshwater fish sampled from five popular fishing spots in Southern California were infected with human-infecting parasites, including Haplorchis pumilio and Centrocestus formosanus. These tiny trematodes can lodge in your intestines and cause everything from severe stomach cramps and diarrhea to dangerous weight loss and, in extreme cases, death.
The culprits? Invasive snails (Melanoides tuberculata) now infest waters in at least 17 states. These snails release larval parasites that burrow into fish flesh, forming cysts. When people eat raw or undercooked fish, the parasites mature inside the human gut.
In some fish—like bluegill and largemouth bass, researchers found thousands of parasites in a single specimen. Disturbingly, many of these parasites concentrate in the tissue surrounding the fins or gills, allowing them to contaminate fillets during cleaning easily.
Equally alarming: scientists found 125 YouTube videos where people prepared and ate these same species raw. Some videos claimed that citrus juice (as in ceviche) “cooks” fish and kills parasites—a dangerous myth. Others showed entire fish heads or organs being consumed, which dramatically increased the risk of infection.
There are no mandatory safety protocols for freezing or treating freshwater fish in the same manner as sushi-grade marine fish. And with no reporting requirements for fishborne parasites in most states, the problem is likely underreported.
Do This: Always freeze freshwater fish at -4°F for 72 hours or cook it thoroughly to a minimum internal temperature of 145°F. That lakeside poke bowl might look fresh, but it could come with a side of parasitic worms.
