Occurrence and prevalence of third-stage larvae of the Anisakidae family in Macrouridae species captured from bathyal depths of Sagami Bay, Japan

Abstract

Anisakiasis is the prevailing form of foodborne illness in Japan, with Anisakidae larvae, specifically Anisakis simplex sensu stricto, serving as its causative agents. These larvae are commonly found in mackerel, sardines, and skipjacks retailed at fresh fish establishments. While the infection rates of Anisakidae larvae in these surface-dwelling fish have been extensively studied, their prevalence in deep-sea fish species remains inadequately understood. This investigation aims to determine the infection rates of Anisakidae larvae in three Macrouridae species—namely Coryphaenoides acrolepis, Coelorinchus japonicus, and Coelorinchus macrochir—which represent the most significant inhabitants of the deep-sea realm. Employing artificial digestion techniques, we successfully retrieved all internal contents of the fish, including the nematode larvae. Some Anisakidae larvae were morphologically identified as A. simplex sensu lato and further identified to species by PCR-RFLP analysis. Two larvae showed a band pattern that appeared to be a hybrid between A. simplex sensu stricto and A. berlandi, which after sequence analysis was considered to be an intraspecific variation of A. berlandi. On the other hand, species considered to be unknown were sequenced and phylogenetic analysis was carried out along with identified larvae. The findings indicate that A. simplex sensu stricto was notably more abundant in C. acrolepis, obtained at a depth of 1000 m. In C. japonicus and C. macrochir, captured at a depth of 400 m, a considerable number of Skrjabinisakis paggiae and Pseudoterranova ceticola, were detected in the deep-sea dwelling Kogia breviceps and K. sima as definitive hosts, were detected. Notably, a single C. macrochir harbored seven species of Anisakidae larvae, with an infection tally of nearly 200 individuals of S. paggiae. Thus, a substantial prevalence of Anisakidae larvae in the deep-sea-dwelling Macrouridae species potentially plays a significant role in the transmission pathway to cetaceans as their final hosts.