Distribution of anisakid nematodes in the muscle tissue of cod (Gadus morhua) from the Norwegian Sea

Atlantic cod (Gadus morhua) is an important commercial fish species on the world market. The aim of our studies was to explore the presence, intensity of infection and distribution of the zoonotic nematodes of the different genera of Anisakidae in the muscle tissue of G. morhua from the Norwegian Sea. Cod from fishing areas FAO IIa1 (n = 50) and FAO IIa2 (n = 56) were sampled in March 2017. The unskinned flesh of each fish was examined using a white-light transilluminator. Collected parasites were identified to the genus level, and a subsample was identified using molecular methods. We found a higher prevalence of infection with Anisakis than with Pseudoterranova in the musculature of cod from both fishing areas. In FAO IIa1, a lower prevalence of infection with Pseudoterranova was recorded (14%) than in FAO IIa2 (∼39%). However, the intensity of infection was higher (53) in FAO IIa2 than in FAO IIa1 (8 parasites per fish). The opposite was found with Anisakis (prevalence 88% in FAO IIa1 and ∼55% in FAO IIa2, intensity up to 30 and up to 25 parasites per fish respectively). Most Anisakis larvae were present in the belly flaps (predominantly the left side), while Pseudoterranova spp. were dispersed with descending frequency in belly flaps, dorsal fillet and caudal fillet. Molecular identification revealed the presence of A. simplex (s.s.), P. decipiens (s.s.) and P. krabbei in both areas, and a hybrid of P. decipiens and P. krabbei in FAO IIa2.