Parasite	Posthodiplostomum sp.
Taxonomy	Plathyhelminthes, Trematoda
Host	Common carp (Cyprinus carpio)
Infection site	Muscle, skin
Clinical signs	White cysts are observed in the muscle (Fig. 1).
Parasitology	The cysts are larvae (metacercariae) of Posthodiplostomum trematode (Fig. 2). The parasite has not been identified at a species level. Some Posthodiplostomum tematodes are known as a causative agent of black spot disease. Generally, Posthodiplostomum trematodes utilize fish as the second intermediate host, preceded by the release from snails (the first intermediate host) and followed by the infection to birds (the definitive host).
Pathology	The pathogenicity to fish may be low.
Health hazard	Posthodiplostomum trematodes parasitizing human have not been reported.
Diagnosis	Check the morphology of the parasite under a flattened preparation.

Fig. 1. Trunk muscle of common carp with metacercaria cysts.

(Photos by T. Awakura)

Fig. 2. Metacercaria of Posthodiplostomum sp.