Study Finds 96% of Tuna Infected With Parasites
A study conducted by scientists at the Federal University of Santa Catarina in southern Brazil has revealed a startling prevalence of parasites in tuna. Researchers examined 53 specimens of skipjack tuna (Katsuwonus pelamis), commonly used in canned goods and sushi worldwide. The findings indicated that 96% of the fish, or 51 out of 53, were infected with numerous parasites, totaling over 1600 worms found across all examined fish. Parasites were discovered in nearly every organ, with only the heart and kidneys remaining unaffected in all specimens. Notably, muscle tissue, the part consumed by humans, contained 441 worms across 51 fish, making it the second most infected area after the intestines.
The study identified two primary types of parasites: Anisakis, a roundworm capable of causing anisakiasis in humans with symptoms like severe abdominal pain, nausea, and vomiting, and Trypanorhyncha, a tapeworm, which rarely infects humans but is unappetizing. For canned fish, industrial production involves thorough inspection, removal of visible parasites, deep freezing at around -20 degrees Celsius for several days, and sterilization by heating above 100 degrees Celsius for 1.5 hours, ensuring parasite elimination.
The situation for raw fish dishes like sushi and sashimi is more complex. While ideally made with fresh fish, this is not always the case outside Japan. In Israel, restaurants serving raw fish must adhere to international sanitary standards, including deep freezing at temperatures as low as -35 degrees Celsius for 15 hours to kill parasites. Chefs also inspect and remove visible parasites during preparation. Therefore, sushi in Western countries from reputable establishments is generally considered safe.
However, preparing sushi at home with store-bought fresh fish carries risks. Some roundworms can attach to the intestinal wall, causing severe gastrointestinal distress. Consumers should inquire if fresh fish has undergone deep freezing and is suitable for raw consumption. Even frozen fish from stores may not have undergone industrial-grade deep freezing sufficient to eliminate live parasites. For homemade sushi, it is recommended to purchase fish confirmed to be industrially disinfected or use alternatives like smoked fish or canned fish.
