The behavior of larvae of Anisakis sp. in North Sea herring (Clupea harengus) after capture was examined by a sensitive quantitative method (digestion). In one winter and one summer experiment, the mean numbers of worms in freshly caught herring were 0.06 and 0.09 (in double fillets), 0.19 and 0.24 (in double belly flaps), and 10.4 and 7.8 larvae (in viscera), respectively. In each experiment herrings were stored ungutted for up to 5 1/2 d on ice (0°C), in refrigerated/chilled sea water (−10°C), or in warm sea water (10°C), but no changes in the numbers of Anisakis larvae in the belly flaps and the fillets could be demonstrated.
The present results show that Anisakis larvae are present in the flesh of herring already at capture, but no significant postmortem migration into the flesh could be demonstrated during storage. Thus, immediately gutting on board cannot eliminate or even reduce the risk from eating raw or inadequately processed herring.