Myxobolus axelrodi n. sp. (Myxosporea: Myxobolidae) a parasite infecting the brain and retinas of the cardinal tetra Paracheirodon axelrodi (Teleostei: Characidae)

Abstract

An investigation of mortalities in a group of cardinal tetras Paracheirodon axelrodi Meyers, 1936, a popular ornamental fish, revealed myxozoan parasites in ventricles of the brains in 3/10 fish and the ocular retina of a fourth. Parasite impacts were unclear, as additional histopathological findings were present, including bacterial dermatitis and meningitis. Ethanol-preserved specimens pooled from multiple fish were used for morphological characterization of myxospores. Elongate, teardrop myxospores were 20.5 ± 0.7-μm (mean ± SD; range = 19.0-21.8 μm) long, 6.6 ± 0.5-μm (5.7-7.9 μm) wide, and 5.1 ± 0.4-μm (4.8-5.9 μm) thick (valvular width). Two, unequally sized, apical, pyriform polar capsules were in the same plane as the sutural ridge. The larger measured 9.9 ± 0.8-μm (8.0-11.2 μm) long and 3.8 ± 0.3-μm (3.2-4.8 μm) wide. The smaller was 4.1 ± 0.3-μm (3.5-4.5 μm) long and 2.0 ± 0.1-μm (1.8-2.3 μm) wide. Identical 1912 bp 18S rRNA sequences were obtained from two pooled spore samples from tetra brains, which did not match any sequences in the NCBI nr/nt database. Phylogenetically, these parasites grouped loosely within a clade containing Myxobolus spp. from other South American characins and Unicauda spp. from siluriform catfish. Myxospores shared some morphological similarities with Myxobolus inaequus from the unrelated glass knifefish (Order: Gymnotiformes), but were genetically divergent (<85 % similarity) from other myxozoan parasites of South American characins and shared few morphological features or tissue predilection sites. Based on host and tissue tropism, spore morphology, and 18S rRNA sequencing, we report this isolate as a previously unknown species, Myxobolus axelrodi n. sp.

Myxobolus freitasi n. sp. (Myxozoa: Bivalvulida), a parasite of the brain of the electric knifefish in the Brazilian Amazon region

“…Myxobolus freitasi n. sp. has a shape similar to that described for other myxozoans of this genus, such as M. axelrodi, described by Camus et al (2017) infecting Paracheirodon axelrodi, M. toyamai, found in Cyprinus carpio in Japan (Yokoyama & Ogawa, 2015) and M. stellatus infecting Thoracocharax stellatus from Colombia (Stilwell et al, 2020).…”

Phylogeny and comprehensive revision of mugiliform-infecting myxobolids (Myxozoa, Myxobolidae), with the morphological and molecular redescription of the cryptic speciesMyxobolus exiguus

“…(Mitchell, 1989; Cone and Overstreet, 1997; Bahri, 2008; Liu et al ., 2010, 2013, 2014, 2015; Zhang et al ., 2014), including M. bizerti from the gills of M. cephalus , and M. exiguus (misidentified as M. muelleri , as previously mentioned) from the mesenteric vessels of C. ramada (e.g. Longshaw et al ., 2003; Eiras et al ., 2005; Kaur and Singh, 2010; Camus et al ., 2017).…”

“…(Mitchell, 1989;Cone and Overstreet, 1997;Bahri, 2008;Liu et al, 2010Liu et al, , 2013Liu et al, , 2014Liu et al, , 2015Zhang et al, 2014), including M. bizerti from the gills of M. cephalus, and M. exiguus (misidentified as M. muelleri, as previously mentioned) from the mesenteric vessels of C. ramada (e.g. Longshaw et al, 2003;Kaur and Singh, 2010;Camus et al, 2017). It has been suggested that the origins and radiations of myxosporean parasites probably reflect the evolution of their fish hosts (e.g.…”

Synopsis of the species of Myxobolus (Cnidaria, Myxozoa, Myxosporea) described between 2014 and 2020

“…Paracheirodon axelrodi (Schultz); fish imported from Brazil to USA Camus et al (2017) M. balatonicus Székely, Molnár et Cech, 2015 P ellipsoidal, 0.6-0.8 × 0.4-0.4 in gill filaments; SP ellipsoidal in frontal view and lemon-shaped in sutural view, sutural protrusion forming a circular rim around spore, emerging about 0.6 to 1.1 over spore surface, 7 distinct sutural edge marks, 10.1-12.2 × 8.8-10.1 × 7.1-7.8; PC equal, slightly converging anteriorly, 4.9-6 × 3-3.7, NC 6; IP large, cuneiform; GBAN: KP205545. Fig.…”