RESUMO
Coccidians are pathogenic protoparasites found in various fish species. In this report, we used light and electron microscopy to study the morphological and ultrastructural features of Calyptospora serrasalmi, a coccidian parasite found to parasitize two additional species of the teleostean genus Serrasalmus, S. striolatus and S. rhombeus, from the Amazon river and the lagoonal region of Recife, Brazil, respectively. Infection involved only the liver parenchyma, with the coccidians occurring as isolated oocysts or in clusters of up to 40-50 oocysts encapsulated by a layer of connective tissue. Several life cycle stages were observed in the same section, with oocysts being the most evident. Each spherical oocyst (~25.5 um in diameter) contained four sporocysts, each surrounded by a thin membranous veil. The sporocysts were pear-shaped (11.8x6.0 um) with an attached apical sporopodium that had several small lateral projections (up to 0.5 um long). These small projections were formed by the same material as the sporocyst wall and were distributed over the basal portion of the wall in 10-12 longitudinal series. The sporocysts lacked a Stieda body and contained two vermiform sporozoites. Calyptospora serrasalmi was distinguishable from previously described species on the basis of sporocyst morphology.