Increasing intensities of Anisakis simplex (Rudolphi, 1809 det. Krabbe, 1878) larvae with weight and sea age in returning adult Atlantic salmon, Salmo salar L., of coastal waters of Norway

Ninety wild Atlantic salmon, Salmo salar L., (1.5-10.3 kg) were caught in the Namsen Fjord near the mouth of River Namsen, mid-Norway, and examined for the presence and distribution of Anisakis simplex (Rudolphi, 1809 det. Krabbe, 1878) larvae by digestion of the viscera and muscles in a pepsin/HCl solution. All salmon were migrating spawners after 1-4 years of feeding in the Atlantic Ocean. All 90 Atlantic salmon had A. simplex larvae in the viscera, and all, except two, had A. simplex larvae in the musculature. The number of A. simplex larvae in each fish varied between 3 and 181, and the total mean number of nematode larvae was 44.5. The intensity of A. simplex larvae was positively correlated with increasing weight and sea age of the host. However, the proportion of larvae in the muscle fillets decreased with increasing host weight and sea age. Atlantic salmon females had more A. simplex larvae than males. In all the fish examined, 70.2% of the A. simplex larvae were found in the viscera and 29.8% in the musculature. The majority (93%) of the larvae in the musculature occurred in the hypaxial sections anterior to the anus. As A. simplex larvae commonly occur in the musculature of wild Atlantic salmon, consumption of unfrozen, raw or semi-raw musculature represents a risk for humans developing anisakiasis.

Automated summary

Ninety wild Atlantic salmon from the Namsen Fjord near the mouth of River Namsen in mid-Norway were found to have A. simplex larvae in their viscera and muscles, with the intensity of larvae positively correlated with the host's weight and sea age. Female salmon harbored more larvae than males, and the majority of larvae were located in the viscera, particularly in the hypaxial sections anterior to the anus.