Scientists from the Federal University of Santa Catarina in Brazil have found that 96 per cent of tuna they examined were infected with parasitic worms, according to a new study.
The researchers collected 53 locally caught skipjack tuna, known scientifically as Katsuwonus pelamis, and dissected each fish in search of parasites. In total they recovered more than 1,600 worms belonging to two genera, Anisakis and Trypanorhyncha.
The parasites were concentrated in three areas of the fish: 596 were found in the intestines, 441 in the muscle tissue, and 408 in the stomachs, the study found.
Health risks from Anisakis worms
One of the parasites identified, Anisakis, is known to pose a direct risk to human health if consumed. 'The nematode can penetrate the human intestinal wall, causing an acute, transient infection characterized by symptoms such as abdominal pain, vomiting, nausea, and/or diarrhea,' the researchers warned.
The team also cautioned that cooking or freezing the fish may not be a reliable safeguard. 'Cooking and/or freezing seafood may not be sufficient to prevent hypersensitivity reactions,' they said, adding that 'thermostable allergens have been detected in extracts, raising questions about the safety of consuming these parasites in cooked fish.'
Why skipjack tuna matters
Skipjack tuna is a staple of the global seafood trade. The researchers noted that the species is 'a fish resource of high economic value and widely used in the fish processing industry, mainly for canned products.' The study, published in the journal Ocean and Coastal Research, aimed to identify the parasitic fauna of the species using morphological methods and to assess the potential impact on both industry and consumers. To examine the fish, the team used Scanning Electron Microscopy, a technique that allows researchers to inspect samples at extremely high magnification.
Fish fraud concerns
The findings come shortly after other scientists warned that tuna, salmon and prawns are sometimes swapped for cheaper substitutes and sold to consumers as premium products. Commonly reported swaps include escolar or cheaper tuna species sold as tuna, less sustainable stocks or rainbow trout sold as salmon, and tilapia sold as red snapper.
Dr Marine Cusa, a marine biologist and policy expert at the Technical University of Denmark, said mislabelling risk varies by species. 'Because mislabelling rates depend on the species, if consumers want to avoid mislabelling then they should avoid certain species and prioritize others,' she said.
She added that white fish such as cod, haddock and saithe are rarely mislabelled in Europe beyond their stated geographical origin, but that 'tuna, swordfish, groupers, snappers, sharks, rays, have a higher species mislabelling risk.'
