Anisakid larva in the viscera of a farmed Atlantic salmon (Salmo salar)

Parasitic nematodes of the family Anisakidae occur in the visceral cavity and surrounding tissues of many marine fish species at a prevalence as high as 100% in wild salmon samples. Human consumption of fish products containing these parasites can result in the zoonotic disease anisakiasis, and Anisakis simplex is most commonly associated with human disease. Previous studies of farmed salmon have found no anisakids in viscera or muscle, presumably because formulated feed production renders parasite larvae nonviable. However, among farmed Atlantic salmon (Salmo salar) examined by histopathology as part of a provincial government auditing program in British Columbia, Canada, 1 of 894 (0.11%) had an anisakid larva partly embedded in the wall of an intestinal cecum. Skeletal muscle is not examined as part of the government's program, but other studies have correlated anisakids in the viscera and muscle. Using anisakid prevalence in viscera as an estimate of its prevalence in muscle, the risk ratio of anisakid parasites in commercial product is 570 times less in farmed than in wild Atlantic salmon.