Ninety-six percent of skipjack tuna examined in a recent study were found to be contaminated with worms, according to research published in the journal Ocean and Coastal Research. Scientists from the Federal University of Santa Catarina analyzed 53 locally caught skipjack tuna, a popular commercial species, and discovered a total of 1,600 parasites.
These parasites were primarily concentrated in the intestines, followed by the muscle tissue – the part commonly consumed by humans – and then the stomach. The kidneys and hearts of the fish remained untainted.
While the presence of parasites in fish is not uncommon, the researchers expressed surprise at the sheer number and widespread distribution of the worms. This finding is particularly concerning given that 3.1 million tons of skipjack tuna were caught and sold globally in 2022.
The study highlights the importance of immediate viscera removal to prevent parasites from migrating from the organs into the flesh. Despite rigorous inspection by seafood processors and chefs, these parasites can be difficult to detect.
The prevalence of such parasites appears to be increasing. A 2020 study by University of Washington researchers found a 283-fold increase in herring worms in raw fish between 1967 and 2017. Herring worms can parasitize various fish and squid species.
Consuming raw or undercooked fish contaminated with these parasites can lead to gastrointestinal issues, including nausea, vomiting, and diarrhea. These symptoms typically subside as the parasites die off within a few days.
Experts recommend thoroughly cooking fish to minimize the risk of parasitic infections. However, some scientists suggest that the presence of parasites can also be an indicator of a healthy ecosystem, implying the fish originated from a natural environment. Chelsea Wood, a parasitologist at the University of Washington, noted that worms in salmon can signal that the fish came from a healthy ecosystem.