Interest in the Myxozoa as significant fish parasites is still increasing with the growing importance of fish farm and wild fisheries around the world. However, little is known about these parasites in South American ornamental fishes, particularly those from the Amazon, where there is a diverse assemblage of several hundred species of live fish. The aim of this study was to evaluate the diversity of myxosporeans parasites of several species of ornamental fish from the Brazilian and Peruvian part of the Amazon basin and its principal tributaries. In this sense, five species of ornamental fish were collected from natural environments (Corydoras melini, Corydoras agassizii, Corydoras leucomelas, Symphysodon discus and Hyphessobrycon loretoensis). Organs infected with myxosporid cyst were removed and examined using differential interference contrast microscopy (DIC). The species of myxosporean were characterized based on light and transmission electron microscopy and with small subunit ribosomal RNA (ssrRNA) gene sequence data. A total of six new myxosporean were found in the analyzed fishes and these species have been identified belonging to the genus Henneguya (three species), Myxobolus (one species), Myxidium (one species), Ceratomyxa (one species) and Unicauda (one species). Considering that the sale of ornamental fish in the Amazon region is responsible for the subsistence of fishing communities in small towns in Amazonian countries and taking into account that international trade in ornamental fishes results in the translocation and distribution of millions of fish around of World, there is a need of constant monitoring of the ornamental fish for diagnosis and timely control of infections by myxosporean aiming to better prevent future disease outbreaks and the risk of transboundary spread of infectious diseases through the dispersal of live specimens.
