A New Species of Ellipsomyxa (Myxozoa: Ceratomyxidae) from the Gall Bladder of the Amazonian Catfish Ageneiosus inermis (Siluriformes: Auchenipteridae)

The fish fauna of the basin of the Amazon River is one of most diverse of any region on Earth and hosts a parasite fauna that is poorly studied. One group of fish parasites is the Myxosporea, a class of the phylum Cnidaria, which are obligate endoparasites. The present study investigated myxozoans found in specimens of the Neotropical catfish Ageneiosus inermis collected in Marajó Bay, off Humaitá Beach. A total of 25 A. inermis specimens were captured and anaesthetised for necropsy, including the gallbladder, liver and muscle tissue, which were prepared for light microscopy, molecular biology and histology. Plasmodia and spores with morphology typical of the genus Ellipsomyxa were observed in the gallbladders of 14 of the individuals. The disporic plasmodia contain two mature spores measuring 6.6 μm × 4.0 μm, on average, with subterminal polar capsules. The analysis of a partial sequence of the 18 S rDNA gene, together with the morphological and morphometric characteristics of the specimens, supported conclusively the description of a new species of the genus Ellipsomyxa. This is the first record of a species of this genus parasitising A. inermis. This represents the first record of a species of this genus parasitizing A. inermis and describes a new taxon.