Abstract
A new microscopic cnidarian is described, infecting five of thirty (16.6%) specimens of Corydoras schwartzi caught in the Purus River, State of Amazonas, Brazil. Histological analysis showed that cyst development occurred in the serosa layer of the intestine. Mature myxospores are ovoid in body shape in frontal view, 22.4 ± 0.3 μm in total length and 16.3 ± 0.1 μm in width. Internally, two aubergine-shaped, elongate symmetrical polar capsules occupy more than half the length of the spore, 14.3 ± 0.2 μm in length and 6.5 ± 0.1 μm in width. Ultrastructural analysis provided evidence of five polar filament coils inside the polar capsule and binucleated sporoplasm containing a moderate number of sporoplasmosomes. The valvogenic cells abutting each other form a sutural ridge and frequently a thin layer of homogeneous material separates the cells. The outer surface of the myxospore valves is smooth, with no evidence of formation of ridges in the valves. Immature myxospores in various stages of development were observed. This study is the first report of a myxosporean parasitizing C. schwartzi and the first report of a myxosporean infection in the intestine of an ornamental fish from South America.
Highlights
Within Phylum Cnidaria, myxozoans are microscopic endoparasites of worldwide distribution and with approximately 2400 species they represent around 20% of cnidarian species diversity (Zhan et al 2013; Atkinson et al 2018)
The present study describes a new species of Myxobolus Bütschli, 1882 infecting the intestine of C. schwartzi from Lábrea Municipality in the Amazon region of Brazil, a key supply region of this species to international aquarium markets
Etymology The specific name, adrianoi, is in homage to Dr Edson Adriano, Professor at Federal University of São Paulo, Brazil, who has been contributing to improving our knowledge on the diversity of South American Myxosporea
Summary
Within Phylum Cnidaria, myxozoans are microscopic endoparasites of worldwide distribution and with approximately 2400 species they represent around 20% of cnidarian species diversity (Zhan et al 2013; Atkinson et al 2018). There are several myxosporean infection surveys of South American teleosts, information on ornamental freshwater fish is still scarce, from the Amazon region (Mathews et al 2018) given the richness in species living in the greatest interconnected freshwater fluvial system in the world (Junk et al 2007; Moreau & Coomes 2007). Within the Amazonian ornamental teleosts, smaller catfishes, species belonging to the genus Corydoras Lacépède, 1803, have great diversity with approximately 162 described species and are of considerable economic importance due to wide commercialization in the international aquarium pet industry (Reis 1998; Prang 2007). It can reach up to 5 cm in total length and inhabits blackwater-flooded forests and the littoral zone of slow flow rivers (Froese & Pauly 2018)
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