Flavobacterium covae is the predominant species of columnaris causing bacteria impacting the channel catfish (Ictalurus punctatus) industry in the southeastern USA

Authors: Lafrentz, Benjamin; KHOO, LESTER - Mississippi State University; LAWRENCE, MARK - Mississippi State University; PETRIE-HANSON, LAURA - Mississippi State University; HANSON, LARRY - Mississippi State University; BAUMGARTNER, WES - Mississippi State University; HEMSTREET, WILLIAM - Auburn University; KELLY, ANITA - Auburn University; Garcia, Julio; Shelley, John; Johnston, Amber; BRUCE, TIMOTHY - Auburn University; GRIFFIN, MATT - Mississippi State University

Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2023
Publication Date: 3/6/2024
Citation: Lafrentz, B.R., Khoo, L.H., Lawrence, M.L., Petrie-Hanson, L., Hanson, L.A., Baumgartner, W.A., Hemstreet, W.G., Kelly, A.M., Garcia, J.C., Shelley, J.P., Johnston, A.E., Bruce, T.J., Griffin, M.J. 2024. Flavobacterium covae is the predominant species of columnaris causing bacteria impacting the channel catfish (Ictalurus punctatus) industry in the southeastern USA. Journal of Aquatic Animal Health. 36:3-15.
DOI: https://doi.org/10.1002/aah.10207

Interpretive Summary: Columnaris disease is one of the largest contributors to disease losses for catfish farmers in the southeastern US. The term ‘columnaris causing bacteria’ (CCB) has been coined in reference to the four described species that cause columnaris disease, Flavobacterium columnare, F. covae, F. davisii, and F. oreochromis. Historically, F. columnare, F. covae, and F. davisii have been isolated from columnaris disease cases in the catfish industry. However, CCBs most severely impacting the industry, as well as their virulence in channel catfish are not fully understood. In this research, the species of CCB involved in 259 columnaris disease cases across Mississippi and Alabama were investigated and the results demonstrated that F. covae is the predominant CCB impacting the catfish industry. Laboratory challenge experiments also demonstrated that on average F. covae causes more mortality in catfish compared to F. columnare and F. davisii. Collectively, these results demonstrate F. covae is the predominant CCB in the US catfish industry and research aimed at developing new prevention and control strategies should target this bacterial species.

Technical Abstract: Columnaris disease is a leading cause of disease related losses in the catfish industry of the Southeastern USA. The term ‘columnaris causing bacteria’ (CCB) has been coined in reference to the four described species that cause columnaris disease, Flavobacterium columnare, F. covae, F. davisii, and F. oreochromis. Historically, F. columnare, F. covae, and F. davisii have been isolated from columnaris disease cases in the catfish industry; however, there is a lack of knowledge of which CCB species are most prevalent in farm-raised catfish. The current research objectives were (1) sample columnaris disease cases from the US catfish industry and identify species of CCB involved, and (2) determine the virulence of the four CCB species in channel catfish in controlled laboratory challenges. Bacterial isolates or swabs of external lesions from catfish were collected from 259 columnaris disease cases in Mississippi and Alabama from 2015-2019. DNA extracted from the samples were analyzed using a CCB-specific multiplex PCR to identify the CCB present in each diagnostic case. Results demonstrated that F. covae is the predominant species of CCB impacting the US catfish industry, present in 94.2% (n = 244) of diagnostic case submissions. Challenge experiments demonstrated F. covae and F. oreochromis were highly virulent to channel catfish resulting in near 100% mortality for most isolates. In contrast, F. columnare and F. davisii were less virulent resulting in less than 40% mortality for most isolates. Collectively, these results demonstrate F. covae is the predominant CCB in the US catfish industry and research aimed at developing new control and prevention strategies should target this bacterial species. The methods described herein can be used to continue monitoring the prevalence of CCB in the catfish industry and can be easily applied to other industries to identify which Flavobacterium species have the greatest impact.