Infection of the Japanese common squid, Todarodes pacificus (Cephalopoda: Ommastrephidae) by larval anisakid nematodes

The Japanese common squid (Todarodes pacificus) is a commercially important species comprising two main cohorts (autumn and winter) that have different feeding areas and migration routes. This study examined temporal and geographical differences in the infection of the two cohorts by larval anisakid nematodes. Squids were infected by two species: Anisakis simplex s.l., which was found on the outside walls of the stomach and caecum of the squids, and Lappetascaris sp., which was found in the anterior end of the mantle. The prevalence of A. simplex s.l. was higher in the winter cohort than in the autumn one, presumably because the winter cohort forages in the Sea of Okhotsk and the Oyashio regions (northwest Pacific Ocean), where infection by A. simplex s.l. in walleye pollock (Theragra chalcogramma) is high, while the autumn cohort does not migrate to these areas. The prevalence of Lappetascaris sp. was high in both cohorts at the feeding grounds near Hokkaido in northern Japan, which suggests this is where infection occurred.