New data on Henneguya postexilis Minchew, 1977, a parasite of channel catfish Ictalurus punctatus, with notes on resolution of molecular markers for myxozoan phylogeny

Authors: WOODYARD, ETHAN - Mississippi State University; ROSSER, THOMAS - Mississippi State University; STILLWELL, JUSTIN - University Of Georgia; CAMUS, ALVIN - University Of Georgia; KHOO, LESTER - Mississippi State University; Waldbieser, Geoffrey - Geoff; LORENZE, WALTER - University Of Georgia; GRIFFIN, MATT - Mississippi State University

Submitted to: Systematic Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2021
Publication Date: 1/14/2022
Citation: Woodyard, E.T., Rosser, T.G., Stillwell, J.M., Camus, A.C., Khoo, L.H., Waldbieser, G.C., Lorenze, W.W., Griffin, M.J. 2022. New data on Henneguya postexilis Minchew, 1977, a parasite of channel catfish Ictalurus punctatus, with notes on resolution of molecular markers for myxozoan phylogeny. Systematic Parasitology. 99(1):41-62. https://doi.org/10.1007/s11230-021-10015-3.
DOI: https://doi.org/10.1007/s11230-021-10015-3

Interpretive Summary: Infections by myxozoan parasites can cause significant production losses in the US catfish industry, such as Proliferative Gill Disease (PGD) which accounts for 10 - 30% of annual catfish diagnostic cases. Ten species within the genus Henneguya have been described from infections in channel catfish. While there is substantial evidence that blue x channel hybrid catfish are dead-end hosts in the H. ictaluri life cycle, other Henneguya species may be implicated in PGD outbreaks in hybrid catfish. Histological data and genomic DNA sequence was obtained from Henneguya postexilis in order to better define this species and refine current diagnostic tools. The new tools will be useful for elucidating the life cycle of H. postexilis and determining its role in catfish morbidity and mortality.

Technical Abstract: Previous morphological and histological data are supplemented with molecular and ultrastructural data for a Henneguya sp. isolated from farm-raised channel catfish Ictalurus punctatus in Mississippi, USA. Myxospores were cryptic, encapsulated within a thin layer of epithelium in the gill lamellae with spore measurements consistent with the original description. Myxospores were 42.7–49.1 µm in total length with spore bodies 12.1–17.2 × 3.6–4.8 × 2.9–3 µm. Polar capsules were of unequal length, with the longer capsule being 4.4–6.7 × 1.1–1.6 µm and the shorter capsule being 4.4–6.4 × 1.1–1.6 µm. Polar filaments had 6–8 turns. Caudal processes were 25.7–38.1 µm in length. Spores were encapsulated in a thin layer of epithelium in the gill lamellae. Molecular data from the most commonly used markers for myxozoan identification and phylogeny, partial 18S small subunit ribosomal gene (SSU), partial 28S large subunit ribosomal gene (LSU), and elongation factor 2 (EF2) were generated for H. postexilis. Additionally, novel data for LSU and EF2 were generated for archived myxozoan specimens from farm-raised catfish (H. mississippiensis, H. ictaluri, H. exilis, H. adiposa, H. sutherlandi, H. bulbosus, Unicauda fimbrethilae), as well as archived specimens from wild fish (H. laseeae [from Pylodictis olivaris], Hennegoides flockae [from Aphredoderus sayanus], Myxobolus cloutmani [from Cycleptus elongatus]. These include the first EF2 sequence data for the genera Hennegoides and Unicauda. Phylogenetic analyses using these data placed H. postexilis in well supported clades with other ictalurid-infecting Henneguya species. Phylogenetic signal assessments on these analyses suggest that while SSU provided the greatest phylogenetic signal, LSU yielded comparable signal, supporting previous work implying this region may be underutilised in reconstructing myxobolid phylogenies.