A novel Ceratomyxa species (Myxozoa: Cnidaria) infecting an Amazonian catfish

Morphological and molecular characterization of a new freshwater Ceratomyxa species (Cnidaria: Myxozoa) from the yellow catfish, Trachysurus fulvidraco in China

Ceratomyxa Thélohan, 1892 is one of the largest genera of the sub-phylum Myxozoa, and has a worldwide geographical distribution. Ceratomyxa species mainly infect the gallbladder of marine fish and rarely infect histozoically or coelozoically freshwater fish. In the present study, yellow catfish, Trachysurus fulvidraco (Siluriformes, Actinopteri) collected from the low reach of Yellow River was first found to be infected with an unknown Ceratomyxa species in their gallbladder which was identified to be new to science and nominated as Ceratomyxa huangheensis n. sp. by an integrative taxonomic approach for myxosporeans. Spores are typical of the genus Ceratomyxa, and matures spores are arcuate, with posterior angle of 139.2 ± 11.6 (137.0-156.0)° and rounded ends, and measures 4.7 ± 0.6 (3.3-5.5) μm in length, and 10.7 ± 1.3 (8.5-13.3) μm in thickness. Two spore valves are slightly unequal and present elongated ovoid in the lateral view. Two equal spherical polar capsules, measuring 2.2 ± 0.4 (1.4-2.8) μm × 2.0 ± 0.4 (1.0-2.5) μm in size locates adjacent to the straight suture line. The obtained partial small subunit ribosomal DNA (SSU rDNA) sequence was unique among all myxozoans in GenBank, and the highest similarity is 85.3% with Ceratomyxa sparusaurati, a marine fish-infecting congener. Phylogenetic analysis further indicated that this novel species did not cluster with other freshwater fish-infecting congeners from South America to form an independent clade, but was phylogenetically positioned within the marine fish-infecting clade. The possible presence of different radiation trajectories between Ceratomyxa huangheensis n. sp. and Amazonian freshwater Ceratomyxa lineage was discussed. This is the first report of Ceratomyxa species in the Yellow River basin and the second freshwater Ceraotomyxa species in China, even in Asia.

A new freshwater Ceratomyxa species (Myxozoa: Ceratomyxidae) parasitizing a sciaenid fish from the Amazon Basin, Brazil

Myxozoans of Ceratomyxidae Doflein, 1899 are common coelozoic parasites of marine life, and are also found less frequently in freshwater fish. The present study describes Ceratomyxa ranunculiformis n. sp. as a new freshwater myxosporean species infecting the gall bladder of the Amazonian sciaenid Plagioscion squamosissimus. The new Ceratomyxa was described based on its host, myxospore morphology, ribosomal rDNA gene sequencing, parasite distribution, and phylogenetic analysis. Immature and mature plasmodia were tadpole-shaped or pyriform, and exhibited slow undulatory motility. The myxospores were elongated and crescent-shaped in the frontal view, with a sutural line between two valves, which had rounded ends. The measurements of the formalin-fixed myxospores were: average length 4.9 (4.0-6.6) μm, average thickness 37.6 (32.4-43.9) μm, average posterior angle 165° (154°-173°). Two ovoid polar capsules of equal size, average length 2.0 (1.4-3.0) μm and average width 1.9 (1.4-2.4) μm, were located adjacent to the suture and contained polar filaments with 2-3 coils. The integrated comparative analysis of the morphological characteristics and molecular analyses of the ribosomal rDNA genes supported the identification of a new species of coelozoic Ceratomyxa. Maximum likelihood analyses showed the new species clustering within a well-supported clade, together with all the other Amazonian freshwater ceratomyxids.

Occurrence of the host-parasite system Rhaphiodon vulpinus and Ceratomyxa barbata n. sp. in the two largest watersheds in South America

While around world, species of the genus Ceratomyxa parasite majority marine hosts, growing diversity has been reported in South American freshwater fish. The present study reports Ceratomyxa barbata n. sp. parasitizing the gallbladder of the Rhaphiodon vulpinus fish from the Amazon and La Plata basins. Morphological (light and transmission electron microscopy), molecular (sequencing of small subunit ribosomal DNA - SSU rDNA), and phylogenetic analyses were used to characterize the new species. Worm-like plasmodia endowed with motility were found swimming freely in the bile. The myxospores were elongated, lightly arcuate, with rounded ends and had polar tubules with 3 coils in the polar capsules. Ultrastructural analysis revealed plasmodia composed of an outer cytoplasmic region, where elongated tubular mitochondria, a rough endoplasmic reticulum, sporogonic stages, and a large vacuole occupying the internal area were observed. Phylogenetic analysis, based on SSU rDNA, found that among all South America freshwater Ceratomyxa species, C. barbata n. sp. arises as an earlier divergent species. The present study reveals the occurrence of this host-parasite system (R. vulpinus/C. barbata n. sp.) in the two largest watersheds on the continent.