August 7, 2025
August 7, 2025
Dr. Abigail Armwood
College of Veterinary Medicine, North Carolina State University
1Samantha J. Oakey, 1Chareerut Phruksaniyom, 2Shay Kashey, 2Lori S.H. Westmoreland, 2Emily F. Christiansen, 2Sonya Carlson, 3Bridgette K. Gunn, 3John H. Leary, 3Alvin C. Camus, 4Marine Combe, 4Théo Deremarque and 1Abigail R. Armwood
1College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, Raleigh, NC 27606; 2North Carolina Aquarium Pine Knoll Shores, 1 Roosevelt Boulevard, Pine Knoll Shores, NC, 28512; 3College of Veterinary Medicine, University of Georgia, 501 D.W. Brooks Drive, Athens, GA, 30602, 4Institute of Evolutionary Science of Montpellier (ISEM), University of Montpellier, campus Triolet, 34095 Montpellier cedex 05, France, Buildings 21, 22 et 24
Striped shiners (Luxilus chrysocephalus) are a keystone species in North Carolina, USA with collaborative and permitted efforts enacted to breed this species in captivity for eventual release. In May 2023, striped shiners, wild-caught in Cane River Park, North Carolina, were transported to the North Carolina Aquarium at Pine Knoll Shores to breed. The first batch of juveniles were captive-hatched in August 2023 and few developed spinal deformities. Four affected juvenile striped shiners were euthanized in January 2024, fixed whole in 10% neutral buffered formalin, and submitted for histopathology to North Carolina State University. Whole fish were processed routinely for histological evaluation and stained with haematoxylin and eosin (H&E) and select special stains. Based on histopathologic findings, RNAscope® in situ hybridization (ISH) and qPCR targeting Sphaerothecum destruens 18S rRNA were performed on affected shiners. The ITS-1 gene was sequenced from positive samples, and compared to known S. destruens sequences for genetic analysis. The initial wild-caught broodstock produced a second juvenile batch, and qPCR was performed on eggs or larvae either individually (n = 22) or pooled (n = 189). Additionally, histopathology (n = 5) and qPCR (n = 10) were performed on survivors of the first juvenile group in February 2025. Grossly, the initial four submitted fish exhibited marked kyphosis and scoliosis. Histopathologically, discrete granulomas composed of epithelioid macrophages were disseminated throughout most tissues. The epithelioid macrophages contained variable numbers of 1-3 µm in diameter, brightly eosinophilic, round spores with basophilic nuclei. Spores stained positively with Grocott-Gomori’s methenamine silver (GMS), periodic acid Schiff and negatively with Ziehl-Neelsen acid-fast and Gram. These individuals tested positive for S. destruens via ISH and qPCR. Preliminary ITS-1 sequence analysis suggests these Sphaerothecum destruens strains are more closely related to strains found in Asia and Europe than to those previously identified in the USA. Additional fish (n = 9) from this first captive-hatched batch continued to test qPCR positive as of February 2025 with histology revealing numerous similar granulomas often with 1-3 µm in diameter, basophilic, refractile, GMS-positive organisms, presumed to represent degenerate S. destruens. No S. destruens was detected in the broodstock’s second batch of eggs and larvae using qPCR. Sphaerothecum destruens is a mesomycetazoan of concern within US salmonid populations and European and Asian wild cyprinids with mortality rates reaching 100% in certain species. The strain similarity to those in Europe and Asia suggests introduction into the US through a nonnative carrier fish host. The significance of this introduction remains unclear, but relating to the European disease progression may foreshadow eventual population declines in key native cyprinids. Preliminary evidence based on diagnostic submissions from another institution suggests these agents may be more widespread in North Carolina and warrants further investigation in Southeastern waterways.
Dr. Al Camus
College of Veterinary Medicine, University of Georgia, Athens, GA
Ashley L. Powell1, Abigail R. Armwood2, Mark D. Fast3, Matt J. Griffin4,5, Alvin C. Camus1
1College of Veterinary Medicine, University of Georgia, Athens, GA; 2College of Veterinary Medicine, North Carolina State University, Raleigh, NC; 3Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, Canada; 4Aquatic Research and Diagnostic Laboratory, College of Veterinary Medicine, Thad Cochran National Warmwater Aquaculture Center, Delta Research and Extension Center, Mississippi State University, Stoneville, MS
Domestic catfish farming involves the culture of both channel (Ictalurus punctatus) and channel ♀ x blue (Ictalurus furcatus) ♂ hybrid catfish. While not grown commercially, male blue catfish are reared to produce the hybrid cross. One of the most significant industry challenges is management of bacterial diseases, including Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish (ESC) and E. piscicida. While the two bacterial species are estimated to directly cost the industry $5.2–17.6 million US annually, the two catfish species and their hybrid cross exhibit marked differences in their susceptibilities to the bacterial agents, with E. ictaluri epizootics occurring primarily in channel catfish and E. piscicida in hybrids. As a result, research into the immune responses of catfish to these pathogens is imperative given the differences in susceptibility, lack of an effective E. piscicida vaccine, limited availability of approved antibiotics for use in aquaculture, and increasing concern over antimicrobial resistance. The objectives of this proposed research project are to: 1) compare and characterize the immunological responses of channel, hybrid, and blue catfish to infection with E. ictaluri and E. piscicida at 24-hours post-challenge and peak mortality using bulk RNA-sequencing, 2) compare and characterize immune cell responses of channel and hybrid catfish exposed to E. piscicida at 48-hours post-challenge (peak mortality) using single cell RNA sequencing, and 3) localize host immune responses to various tissues in channel, hybrid, and blue catfish exposed to E. ictaluri and E. piscicida using RNAscope® technology. Results of preliminary challenge trials and bulk RNA-sequencing, including differential gene expression and gene ontology enrichment analysis, reveal distinct trends between the three catfish species and will be presented.