The incidence of Anisakis sp. larvae (Nematoda: Ascaridata) in the commercially exploited stocks of herring (Clupea harengus L., 1758,) (Pisces: Clupeidae) in British and adjacent waters.

10 000 herrings from the commercial fisheries around the coasts of Great Britain and Ireland were examined for the nematode larva Anisakis sp. between October 1968 and October 1970. Heavy infestations were found in the North Sea stocks, moderate infestations west of Scotland and minimal infestations elsewhere; but nowhere was the parasite completely absent. Younger fish were often found to be more heavily infested than older fish and it is therefore suggested that the accumulation of larvae in the body cavity may be affected by annual fluctuations either in the population of an infested first intermediate host or in the extent to which the herrings are feeding on this host. A small but constant proportion of the parasites penetrate the musculature of the herring regardless of other factors such as the age or length of the host, or the number of other larvae present.