Novel myxosporean species parasitizing an economically important fish from the Amazon basin.

This paper provides morphological and phylogenetic analyses of two new myxobolid species found infecting Piaractus brachypomus from the Amazon basin. The fish were caught in the Tapajós River, in the municipality of Santarém, in the state of Pará, Brazil. The plasmodial development of Henneguya brachypomus n. sp. occurred in the gill lamellae while Myxobolus pirapitingae n. sp. developed in the pyloric cecum. Morphological analyses did not identify inflammatory infiltrate for either species, but H. brachypomus n. sp. induced stretching of the epithelium, compression of the adjacent tissues, and displacement and deformation of the neighboring lamellae. The mature myxospores of H. brachypomus n. sp. were ellipsoid, with a length of 11.7-13.8 µm, a width of 4.0-4.6 µm, and a thickness of 3.5-4.3 µm. The polar capsules were elongated, with a length of 5.6-7.3 µm and a width of 1.3-2.0 µm, and each contained a polar filament with 8-9 coils. The caudal process was 40.5-48.1 µm long and the total length of the myxospore was 52.4-61.6 µm. Myxobolus pirapitingae n. sp. exhibited rounded mature myxospores measuring 10.0-11.1 µm in length, 7.0-7.6 µm in width, and 5.4-6.3 µm in thickness. The polar capsules were of equal size and occupied less than half the myxospore, measuring 3.5-4.0 µm in length and 2.0-2.6 µm in width, with each containing a polar filament with 6-7 coils. Phylogenetic analysis based on partial small subunit ribosomal DNA (ssrDNA) sequences showed that H. brachypomus n. sp. clustered as a sister species of Henneguya piaractus, while M. pirapitingae n. sp. was grouped in a sub-clade together with Myxobolus matosi and Myxobolus colossomatis.

The resolution of the taxonomic dilemma of Myxobolus colossomatis and description of two novel myxosporeans species of Colossoma macropomum from Amazon basin.

This study presents morphologic, molecular and phylogenetic data about two new species of the genus Myxobolus and of the previously described Myxobolus colossomatis, all which are found infecting the Colossoma macropomum, a fish whose natural habitat is the Amazon Basin of Brazil, from where the specimens for this study were caught. A total of 51 C. macropomum specimens were examined between October of 2014 and January of 2016. Plasmodia of the myxosporeans were found infecting several organs: Myxobolus matosi n. sp. and Myxobolus longissimus n. sp. were respectively found in the inner face of the operculum and in the wall external surface of the stomach and gill arch. M. matosi n. sp. were 9.6 ± 0.4 µm in length, 7.0 ± 0.3 µm in width and 5.0 ± 0.3 µm in thickness of the myxospore. M. longissimus n. sp. measured 19.1 ± 0.4 µm in length, 9.4 ± 0.3 µm in width and 8.3 ± 0.4 µm in thickness. The polar capsules, which were elongated, showed 4.3 ± 0.4 µm in length and 1.9 ± 0.1 µm in width for M. matosi n. sp. and 10.5 ± 0.2 µm in length and 2.5 ± 0.1 µm in width for M. longissimus n. sp. The Myxobolus colossomatis had two myxospore morphotypes: 1) Ellipsoidal myxospores measuring 11.6 ± 0.4 µm in length and 7.6 ± 0.2 µm in width. Their elongated polar capsules measured 5.6 ± 0.2 µm in length and 2.5 ± 0.2 µm in width; 2) Oval myxospores measuring 10.4 ± 0.5 µm in length and 7.7 ± 0.3 µm in width. Their polar capsules were 5.4 ± 0.2 µm in length and 2.4 ± 0.0 µm in width. The number of turns of the polar filament was 7-8 coils. The molecular comparison of the small subunit ribosomal DNA (ssrDNA) showed a genetic divergence of 10.3% between M. matosi n. sp. and M. colossomatis, 22.4% between M. matosi n. sp. and M. longissimus n. sp., and 23.2% between M. longissimus n. sp. and M. colossomatis. Myxobolus cf. colossomatis, a parasite of Piaractus mesopotamicus, showed 11.1% of genetic divergence to M. colossomatis, demonstrating them to be distinct species. Phylogenetic analysis, based on sequences of the ssrDNA, showed the M. matosi n. sp. to be a sister species of M. colossomatis, and it also showed M. longissimus n. sp. to be a sister branch in the lineage composed by Myxobolus cf. cuneus and Henneguya pellucida.

Morphological, ultrastructural and phylogenetic analyses of Myxobolus hilarii n. sp. (Myxozoa, Myxosporea), a renal parasite of farmed Brycon hilarii in Brazil.

Myxobolus hilarii n. sp. was described, based on morphology, histology, ultrastructure and 18S rDNA sequencing, infecting the kidney of Brycon hilarii (Valenciennes 1850) (Characiformes: Bryconidae) taken from fish farms in the state of São Paulo, Brazil. Thirteen specimens of B. hilarii were examined and 100% had round, white plasmodia in the kidney. The mature myxospores were rounded, measuring 11.5 ± 0.8 (9.8-13.4) µm in length, 11.0 ± 0.7 (9.7-12.4) µm in width and 7.6 ± 1.0 (6.7-9.0) µm in thickness. Polar capsules were elongated and of equal size, with 6.5 ± 0.4 (6.0-7.2) µm in length and 4.0 ± 0.2 (3.6-5.3) µm in width and their polar filaments had 5 to 7 coils. Histological analysis revealed plasmodial development in the renal tubules, causing compression and deformation of adjacent tissues and destruction of renal tubule cells. Ultrastructural analysis showed direct contact between the plasmodial wall and the host tissue and asynchronous plasmodial development. The phylogenetic analysis of South American myxobolids, based on 18S rDNA sequencing, showed the myxosporeans grouping into two main clades. M. hilarii n. sp. appears as sister species of Myxobolus piraputangae.

Host-parasite and phylogenetic relationships of Myxobolus filamentum sp. n. (Myxozoa: Myxosporea), a parasite of Brycon orthotaenia (Characiformes: Bryconidae) in Brazil.

Myxobolus filamentum sp. n. was found infecting gill filaments of three of 39 Brycon orthotaenia Günther specimens examined (8%), which were taken from the river São Francisco in Minas Gerais state, Brazil. Plasmodia of the parasite were white and long, measuring 5 mm in lenght. Mature spores of M. filamentum sp. n. were oval from the frontal view and biconvex from the lateral view, measuring 7.5-9.7 µm (9.0 ± 0.3 µm) in length and 5.2-7.3 µm (6.2 ± 0.4 µm) in width. The polar capsules were elongated and equal in size, measuring 3.8-5.5 µm (4.7 ± 0.3 µm) in length and 1.3-2.2 µm (1.7 ± 0.1 µm) in width. The development of the parasite led to compression of the adjacent tissues and inflammatory infiltrate with granulocytic cells. Ultrastructural observation revealed that the plasmodia were delimited by two membranes, which had numerous and extensive pinocytotic channels extending into the wide ectoplasm zone. The plasmodial wall exhibited abundant villi-like projections and a thin layer of granular material prevented direct contact between the plasmodial wall and the host tissue. Phylogenetic analysis, based on 18S rDNA, showed M. filamentum sp. n. as a sister species of Myxobolus oliveirai Milanin, Eiras, Arana, Maia, Alves, Silva, Carriero, Ceccarelli et Adriano, 2010, a parasite of other fish species of the genus Brycon Müller et Troschel from South America.