The first report of a fish coccidian parasite, Calyptospora mexicanus n. sp. (Eimeriorina: Calyptosporidae), in Mexico.

The genus Calyptospora is a poorly understood group of coccidian parasites that commonly cause liver infections in fishes from tropical regions. A survey of fishes in different water systems of the Yucatan Peninsula in southern Mexico revealed the presence of an undescribed Calyptospora sp., which infects the pancreatic tissue wedged into the liver of Mayaheros urophthalmus, Parachromis friedrichsthalii, and Rhamdia guatemalensis. The identification of the new species, Calyptospora mexicanus n. sp., was based on morphological and histological data and supported by molecular analyses of the 18S ribosomal RNA gene (rDNA). Sporulated oocysts were spherical in shape, 22.6-29.9 μm diameter, four obovoid to piriform sporocysts 11.8-15.3 μm length × 4.3-6.4 μm width. Each sporocyst is surrounded by a thin membrane veil supported by one sporopodium with 3.9-6.5 μm length, covered with sporopodial projections, and each sporocyst contains two sporozoites. The molecular data indicated 100 % sequence similarity between the sequences obtained from C. mexicanus n. sp. infecting the three fish species and 91.56-97.72 % sequence similarity with the previously reported species (Calyptospora funduli, Calyptospora gonzaguensis, Calyptospora paranaidji, Calyptospora serrasalmi, and Calyptospora sp.). Phylogenetic analysis placed C. mexicanus n. sp. in the family Calyptosporidae, resulting in the first coccidian parasite of fish reported in Mexico.