Echinorhynchus spp

From Fish
E. gadi found in the intestine of Alaska pollack.
Proboscis of E. gadi.

Echinorhynchus spp (e.g. E. gadi) are acanthocephalan parasites that infect the intestinal tract of marine fish.

They have been reportedly found in Alaska pollack (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), littlemouth flounder (Pseudopleuronectes herzensteini), masu salmon (Oncorhynchus masou), Atlantic cod (Gadus morhua), haddock (Melanogrammus aeglefinus)[1].

Life cycle

The parasite body is 10-20 mm long and composed of proboscis, neck and trunk. Worm 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 reported that Echinorhynchus gadi infects to the host through amphipods (Marcogliese, 1994). E. gadi may be composed of genetically isolated sibling species[2].

Clinical signs

Infected fish usually exhibits no external abnormality. Worms (about 10-20 mm) are observed in the rectum.

Since this parasite is not infectious to human, it is harmless in food hygiene.

Diagnosis

Characteristic morphology of the proboscis is observed by flattened preparation. This parasite is mainly reported from wild fish. However, it may become a potential pathogen of cod in mariculture due to the increased population density under farm conditions. Conversely, this parasite has been useful as a biological tag for discriminating stocks of wild cod. [3].

References

  1. Marcogliese, D. J. (1994) Aeginina longicornis (Amphipoda: Caprellidea), new intermediate host for Echinorhynchus gadi (Acanthocephala: Echinorhynchidae). J Parasitol 80:1043-1045
  2. Wayland, M. T., Gibson, D. I. And Sommerville, C. (2005) Morphometric discrimination of two allozymically diagnosed sibling species of the Echinorhynchus gadi Zoega in Muller complex (Acanthocephala) in the North Sea. Syst Parasitol 60:139-149
  3. Khan, R. A. and C. Tuck (1995) Parasites as biological indicators of stocks of Atlantic cod (Gadus morhua) off Newfoundland, Canada. Can J Fish Aquat Sci 52:195-201