Occurrence of Corynosoma cystacanths in commercially distributed marine fish within and outside Hokkaido, Japan.

Acanthocephalans of the genus Corynosoma infect pinnipeds as definitive hosts, using amphipods and decapods as intermediate hosts and various marine fishes as paratenic hosts. Human infection is associated with the consumption of raw marine fishes from Hokkaido, Japan. Widespread distribution of Hokkaido-sourced marine fishes to the greater Tokyo metropolitan area raises concerns about exposure outside Hokkaido. However, data on the prevalence of Corynosoma cystacanths in marine fish marketed in this region remain limited. A total of 473 individuals (24 species) from Hokkaido and 52 individuals (19 species) from outside Hokkaido were examined. Cystacanths were detected in 75 of 473 Hokkaido-sourced fishes (15.9%) across 17 species, with high prevalence in demersal fishes. In contrast, only one cystacanth was detected in non-Hokkaido-sourced fishes, from a specimen of Zeus faber Linnaeus, 1758. Morphological and molecular analyses identified the majority of cystacanths as Corynosoma villosum Van Cleave, 1953, with a smaller proportion as Corynosoma strumosum (Rudolphi, 1802). These findings demonstrate that Corynosoma cystacanths are widely distributed in commercially available marine fishes originating from Hokkaido, and suggest that infection is not restricted to Hokkaido but may occur in low prevalence, in other regions of Japan. Given the global distribution of marine fish trade and the widespread consumption of raw or undercooked seafood, these findings also have broader international implications. Continuous monitoring of commercially distributed marine fishes is therefore important for food hygiene and public health.