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Title: 18S rRNA gene sequencing identifies a novel species of Henneguya parasitizing the gills of the channel catfish (Ictaluridae)

item ROSSER, THOMAS - Mississippi State University
item GRIFFIN, MATT - Mississippi State University
item Quiniou, Sylvie
item KHOO, LESTER - Mississippi State University
item POTE, LINDA - Mississippi State University

Submitted to: Parasitology Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2014
Publication Date: 12/1/2014
Citation: Rosser, T.G., Griffin, M., Quiniou, S., Khoo, L., Pote, L. 2014. 18S rRNA gene sequencing identifies a novel species of Henneguya parasitizing the gills of the channel catfish (Ictaluridae). Parasitology Research. 113(12):4651-4658.

Interpretive Summary: A novel species of Henneguya infecting the gills of channel catfish is described. Molecular and morphological methods were used to characterize the myxospore stage from naturally infected channel catfish. The pseudocysts are large (~1mm diameter), intralamellar, and contain numerous myxospore stages consistent with the genus Henneguya. Histologically, the parasite is unremarkable. Sequencing of the isolate and a subsequent search of the National Centers for Biotechnology Information nucleotide database revealed no identical sequence matches. However, phylogenetic analysis indicated this species grouped with the other known Henneguya that infect ictalurid fish in North America, specifically H. pellis and H. sutherlandi. The unique myxospore morphology, pseudocyst location and morphology, and genetic sequence lead us to propose this as a novel species, H. bulbosus.

Technical Abstract: In the southeastern United States, the channel catfish Ictalurus punctatus is a host to at least eight different species of myxozoan parasites belonging to the genus Henneguya, four of which have been characterized molecularly using sequencing of the small subunit ribosomal RNA gene (SSU rRNA). However, only two of these have confirmed life cycles that involve the oligochaete Dero digitata as the definitive host. During a health screening of farm-raised channel catfish, several fish presented with deformed primary lamellae. Lamellae harbored large, nodular, white pseudocysts 1.25 mm in diameter and upon rupturing, these pseudocysts released Henneguya myxospores, with a typical lanceolate shaped spore body, measuring 17.1 ± 1.0 µm (mean ± SD; range = 15.0-19.3 µm) in length and 4.8 ± 0.4 µm (3.7-5.6 µm) in width. Pyriform shaped polar capsules were 5.8 ± 0.3 µm in length (5.1-6.4 µm) and 1.7 ± 0.1µm (1.4-1.9 µm) in width. The two caudal processes were 40.0 ± 5.1 µm in length (29.5-50.0 µm) with a spore length of 57.2 ± 4.7 (46.8-66.8 µm). The contiguous SSU rRNA gene sequence obtained from myxospores of five excised cysts did not match any Henneguya sp. in Genbank. The greatest sequence homology (91% over 1900 bp) was with Henneguya pellis, associated with blister-like lesions on the skin of blue catfish Ictalurus furcatus. Based on the unique combination of pseudocyst and myxospore morphology, tissue location, host and SSU rRNA gene sequence data, we report this isolate to be a previously unreported species, Henneguya bulbosus sp. nov.