Something's Fishy...
Invasive parasitic worms infect 93% of freshwater fish, making raw consumption risky without proper freezing first.
Read Time: 3 minutes
Published:
- An invasive species of parasitic worm is known to be widespread in freshwater fish in the United States.
- Raw fish should always be properly cleaned and frozen to ensure safe consumption.
Those who fish in lakes and rivers like to show off what they’ve reeled in, and bragging rights have extended to the digital age. TikToks that show off catches-of-the-day garner millions of likes, with popular videos showing fishers turning their boats into kitchens—immediately preparing ceviche or another raw dish with what they’ve caught. But viewers inspired to follow suit should take a moment to pause, as dangerous invasive parasites are wiggling their way into the United States’ freshwater environments.
The FDA requires fish sold for raw consumption to be frozen to kill parasites, but this requirement is difficult, if not impossible, to enforce in fish caught recreationally or sold at unregulated markets. Failure to freeze raw fish can lead to a dangerous infection with parasitic worms (also known as trematodes or flukes) that causes fever, nausea, and pain. Chronic infection from some types of trematodes can lead to organ damage.
Trematodes make their way into freshwater fish and onto our plates by way of commonly invasive red-rimmed melania snails. The snail has spread to all 50 states, introducing two types of the worm to freshwater environments. Emma Palmer and colleagues collected fish from five different freshwater locations in San Diego County, California. They collected over 80 fish, representing seven commonly consumed species. Every species had parasite larvae.
On average, the worms infected 93% of fish in each of the five water sources sampled, shown in different colors on the graph below. As displayed, bluegill and largemouth bass had the highest amounts of parasites, with one type of worm (measured in the top two boxes) infecting the entire population in some localities. The larger the fish, the more trematodes.
The researchers also provided context for their findings by analyzing social media data to understand why people eat raw freshwater fish. They watched over 100 YouTube videos that documented people consuming raw freshwater fish for culinary purposes or “shock factor.” The videos often contained false claims such as that marinating the fish in citrus juice or eating a fish caught in clean water means it is parasite-free.
Palmer and colleagues call for public education to inform fishers of the risks of underpreparing their catches and suggest sharing safety guidelines more broadly. Immediately and properly freezing fish (commercial freezers are often recommended), cutting the fish on clean surfaces, and keeping the dishes chilled until it’s time to eat allow fishers to safely serve what they’ve reeled in.
