Nybelinia spp

From Fish
Nybelinia (arrows)in the peritoneal cavity of Alaska pollack
Nybelinia (arrows) in Japanese common squid.
A plerocercoid larva of N. surmenicola

Nybelinia spp are cestode tapeworms that parasitise marine fish such as Alaska pollack (Theragra chalcogramma) and Japanese common squid (Todarodes pacificus). They infect the peritoneal cavity, mantle cavity, and muscles.

Life cycle

Plerocercoid larvae of Nybelinia surmenicola are encysted by host’s tissues in fish and squids. The worm (about 5-10 mm) has 4 tentacles at the apical end of the head (Fig. 3). The tentacle is armed with hooks, which arrange spirally, and plays a role of an anchor. N. surmenicola utilizes krill as the intermediate host, fish as the paratenic host and salmon shark Lamna ditropis as the definitive host[1].

Clinical signs

No external signs are evident. Rice bean-shaped parasites are observed in the viscera and peritoneal cavity.

The pathogenicity to fish host is low. Since this parasite is not infectious to human, it is harmless in food hygiene. In rare cases, this parasite sticks to the back of the human throat, but this can be readily removed by forceps.

Diagnosis

Diagnosis is based on detectiom of larvae which possess characteristic 4 tentacles at the apical end of the scolex. N. surmenicola is often utilized as a biological tag to discriminate fish populations because of its high abundance and a low pathogenicity[2].

References

  1. Shimazu, T. (1975) A description of the adult of Nybelinia surmenicola with discussions on its life-history (Cestoda: Trypanorhyncha: Tentaculariidae). Bull Jap Soc Sci Fish 41:823-830
  2. Blaylock, R. B., L. Margolis and J. C. Holmes (2003) The use of parasites in discriminating stocks of Pacific halibut (Hippoglossus stenolepis) in the northeast Pacific. Fishery Bulletin 101:1-9