{"id":261,"date":"2025-06-03T13:27:19","date_gmt":"2025-06-03T13:27:19","guid":{"rendered":"https:\/\/scienceblog.com\/wildscience\/?p=261"},"modified":"2025-06-03T13:27:19","modified_gmt":"2025-06-03T13:27:19","slug":"think-your-freshwater-fish-is-safe-93-carry-parasites-that-can-infect-humans","status":"publish","type":"post","link":"https:\/\/scienceblog.com\/wildscience\/2025\/06\/03\/think-your-freshwater-fish-is-safe-93-carry-parasites-that-can-infect-humans\/","title":{"rendered":"Think Your Freshwater Fish Is Safe? 93% Carry Parasites That Can Infect Humans"},"content":{"rendered":"

More than 90% of popular freshwater game fish in Southern California harbor invasive parasites capable of infecting humans, according to new research from UC San Diego’s Scripps Institution of Oceanography. The study, published in the Journal of Infectious Diseases<\/a>, reveals that fish species frequently caught and eaten by Americans carry large numbers of parasitic worms that can cause gastrointestinal problems, weight loss, and in severe cases, strokes or heart attacks.<\/p>\n

The parasites\u2014two species of flatworms called trematodes\u2014arrived in the United States more than a decade ago inside invasive snails from Southeast Asia. Now they’ve spread to fish that millions of Americans catch and eat, creating what researchers call a previously unrecognized public health risk.<\/p>\n

The Hidden Threat in Your Catch<\/h2>\n

“Americans don’t usually think about parasites when they eat freshwater fish because it hasn’t historically been an issue here,” said Ryan Hechinger, an ecologist and parasitologist at Scripps and the study’s senior author. “But these trematodes have now been widely introduced in the U.S. and that means that doctors and the public should be aware.”<\/p>\n

The researchers examined 84 fish from seven different species, including largemouth bass and bluegill, collected from five popular fishing locations in San Diego County during 2023. Their findings were stark: 93% of all fish contained Haplorchis pumilio parasites, with some individual fish harboring thousands of the microscopic invaders.<\/p>\n

A second parasite, Centrocestus formosanus, infected 91% of fish at two of the five locations where it was present. Both parasites originally infected people in Southeast Asia before hitchhiking to America inside red-rimmed melania snails, which have now spread to 17 states and Puerto Rico.<\/p>\n

How Fish Become Mobile Parasite Hotels<\/h2>\n

The trematodes follow a complex three-host lifecycle that transforms fish into unwitting carriers. Free-swimming parasite larvae exit infected snails and burrow into fish tissue, forming protective cysts called metacercariae. These infectious stages concentrate in different parts of the fish depending on the species\u2014Haplorchis pumilio embeds primarily in fin bases and surrounding muscle tissue, while Centrocestus formosanus prefers gills.<\/p>\n

What makes this particularly concerning is the parasite load. One bluegill collected during the study contained 16,973 Haplorchis pumilio and 8 Centrocestus formosanus larvae. Even fish that appear perfectly healthy can harbor hundreds or thousands of parasites without showing any visible signs of infection.<\/p>\n

YouTube Videos Reveal Risky Eating Habits<\/h2>\n

The researchers didn’t stop at examining fish. They analyzed 125 YouTube videos with nearly 5 million combined views to understand how Americans actually prepare and eat freshwater fish. The results were troubling: 65% of videos showed people consuming raw, unfrozen fish\u2014exactly the conditions that allow parasites to survive and infect humans.<\/p>\n

“Nearly 5 million views shows there is widespread interest and possibly a widespread practice of folks eating freshwater fish raw,” said Emma Palmer, a marine scientist at the Smithsonian Environmental Research Center who conducted the study during her graduate studies at Scripps.<\/p>\n

Many videos promoted dangerous misconceptions about food safety. Common myths included claims that citrus marinades “cook” fish and kill parasites, that healthy-looking fish are safe to eat raw, or that visual inspection can detect parasites. None of these beliefs are scientifically accurate.<\/p>\n

Key Study Findings:<\/h3>\n