Glugea plecoglossi

From Fish
Many xenomas are observed in the body cavity of ayu.
Artificially produced seedlings of ayu infected with Glugea
Fresh spores of G. plecoglossi

Glugea plecoglossi is a microsporidian parasite found in the peritoneal cavity of marine fish, Ayu (Plecoglossus altivelis) and rainbow trout (Oncorhynchus mykiss).

Many spores are produced inside xenomas (a complex formed by a host cell and a parasite). A spore (average length 5.8 mm; average width 2.1 mm) is ellipsoidal. Spores are ingested by the host's phagocytic cells and develop inside the cells. These cells begin to hypertrophy, take a nutrition from the host and result in xenomas. When the xenoma establishes on the wall of the peritoneal cavity, it is encased by the host's connective tissues. The parasite proliferates, and fills up the xenoma. Xenoma, a few mm (up to 5 mm) in size, is visually observed as a cyst[1].

Clinical signs

Infected fish exhibits no significant external abnormalities, while the abdomen is filled with numerous Glugea cysts (ca. 4-5 mm). On the other hand, in heavily infected fry of ayu, cysts are easily observed by transmitted light even without dissection.

In a heavy infection, diseased fish sometimes exhibits ascites and emaciates, but few fish die.

Since this parasite is not infectious to human, it is harmless in food hygiene[2].

Diagnosis

Diagnosis can be determined by observation of Glugea cysts in the peritoneal cavity. For confirmation, check the spores by the wet-mount of xenomas. The sample should be smeared and stained by Uvitex 2B followed by a fluorescent microscopic observation. The stained spores emit blue fluorescence under UV radiation.

Treatment

To prevent the disease effectively, maintain the fish at 28-29 C. for 5 days, then return to the normal temp. for 7 days, and raise to 28-29 C. for 5 days again before the fish develops the disease, e. g. just after the introduction of wild seedlings. Take care of other diseases or progress of the sexual maturation when maintaining at high temperature.

References

  1. Takahashi, S. (1981) Studies on Glugea infection of ayu, Plecoglossus altivelis. Bull Shiga Pref Fish Exp Station 34:1-81
  2. Takahashi, S. and K. Ogawa (1997) Efficacy of elevated water temperature treatment of ayu infected with the microsporidian Glugea plecoglossi. Fish Pathol 32:193-198