New parasite discovered in Metynnis

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Parasitologists have described a new species of myxozoan fish parasite from a South American characid fish.

Casal, Matos and Azevado of Portugal's High Institute of Health Sciences described the new species Myxobolus metynnis after finding the parasites living in the skin of the Silver dollar, Metynnis argenteus. Their results were published recently in the Journal of Parasitology.

The authors collected M. argenteus in the the lower Amazon River, near the city of Peixe Boi, Par State, Brazil, and discovered several life stages of the parasites in the connective subcutaneous tissues of the fish.

The authors wrote: "Polysporic, histozoic plasmodia were delimited by a double membrane with numerous microvilli on the peripheral cytoplasm. Several life-cycle stages, including mature spores, were observed.

"An envelope formed by numerous fine and anastomosed microfibrils was observed at the spore surface. The spore body presented an ellipsoidal shape and was about 13.1 microm long, 7.8 microm wide, and 3.9 microm thick.

"Elongated-pyriform polar capsules were of equal size, measuring 5.2 microm in length, 3.2 microm in width, and possessing a polar filament with 8-9 turns around the longitudinal axis.

"The binucleated sporoplasm contained a vacuole and numerous sporoplasmosomes. These were circular in cross-section, showing an adherent eccentric, dense structure, with a half-crescent section."

Myxozoan parasites seem common on members of the Metynnis genus imported from South America.

For more information on the new parasite see the paper: Casal G, Matos E, Azevedo C (2006) - A new myxozoan parasite from the Amazonian fish Metynnis argenteus (Teleostei, Characidae): light and electron microscope observations. J Parasitol. 2006 Aug ; 92(4): 817-21