| Parasite | Longicollum pagrosomi |
|---|---|
| Taxonomy | Acanthocephala, Palaeacanthocephala, Echinorhynchida |
| Hosts | Red sea bream (Pagrus major), tiger puffer (Takifugu rubripes) |
| Infection site | Rectum |
| Clinical sign | Infected fish usually exhibits no external abnormality. However, some heavily infected fish show rectal prolapse, abdominal swelling and reddening around the anal. Longicollum pagrosomi (10-20 mm) is observed in the rectum. |
| Parasitology | The body is 10-20 mm long and composed of proboscis, neck and trunk. The parasite burrows into the rectum wall of the host with its proboscis and neck. It is dioecious and females produce ellipsoidal eggs including embryos. Larvae are hatched from eggs inside the adult body and grow to be encysted cystacanth. Generally, acanthocephalans utilizing fish as the definitive host and parasitize crustaceans for the intermediate host. It was indicated by the infection experiment that Longicollum pagrosomi infects to red sea bream through amphipods (Yasumoto and Nagasawa, 1996). |
| Pathology | Heavily infected fish shows growth retardation and sometimes die following to abdominal swelling and procidentia. Degeneration of the rectum tissue and inflammation are observed. The host’s tissues encase the anterior part of the parasite and form granuloma (Hatai et al., 1987). |
| Health hazard | Since this parasite is not infectious to human, it is harmless in food hygiene. |
| Diagnosis | A parasite can be visually observed in the rectum. |
| Other information | Cage-cultured red sea bream are often infested with this parasite because the fish feed on amphipods attaching to the net-cage. Therefore, changes or washes of the net are effective control methods for this disease. |
| References | Hatai, K., Horita, Y. and S. Kubota (1987): A histopathological study on
longicollosis in cultured red sea bream, Pagrus major. Fish Pathol.,
22, 31-32. (In Japanese) Yasumoto, S. and K. Nagasawa (1996): Possible life cycle of Longicollum pagrosomi and acanthocephalan parasite of cultured red sea bream. Fish Pathol., 31, 235-236. |
Fig. 1. L. pagrosomi found in red sea bream.
(Photo by K. Nagasawa)