Fig. 1. Hirudinellida from Norythern bluefin tuna.

Parasite	Hirudinellidae
Taxonomy	Plathyhelminthes, Trematoda, Azygiida
Hosts	Northern bluefin tuna (Thunnus thynnus), wahoo (Acanthocybium solandri)
Infection site	Digestive tract
Clinical sign	A dusky-red encysted metacercaria (ca. 1 cm) is observed in the digestive tract.
Parasitology	Excysted parasite is ca. 1 cm in size (Fig. 1).
Pathology	No report.
Health hazard	Since this parasite is not infectious to human, it is harmless in food hygiene.
Other information	This parasite principally encysts in the stomach of wahoo. Therefore, it is considered that the parasite invades Northern bluefin tuna by accident.。