Plesiomonas shigelloides as an emerging pathogen in catfish aquaculture: a case from a South Texas commercial farm

Authors: MOHAMMED, HAITHAM - Texas A&M University; ELBANNA, NOHA - Texas A&M University; ERDOGAN, OZGUR - Texas A&M University; Aarattuthodi, Suja; TEKEDAR, HASAN - Mississippi State University; ABDELHAMED, HOSSAM - Mississippi State University; DIAZ-DELGADO, JOSUE - Texas A&M University

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2026
Publication Date: 1/8/2026
Citation: Mohammed, H.H., Elbanna, N.I., Erdogan, O., Aarattuthodi, S., Tekedar, H.C., Abdelhamed, H., Diaz-Delgado, J. 2026. Plesiomonas shigelloides as an emerging pathogen in catfish aquaculture: a case from a South Texas commercial farm. Microorganisms. 14(1). https://doi.org/10.3390/microorganisms14010144.
DOI: https://doi.org/10.3390/microorganisms14010144

Interpretive Summary: Catfish farming represents the largest sector of U.S. aquaculture, contributing approximately 70% of the total finfish aquaculture production and playing a vital role in the domestic economy. The top four catfish-producing states -Mississippi, Alabama, Arkansas, and Texas- account for 95% of the nation's total catfish sales. Infectious diseases pose a serious threat to catfish farming, with bacterial pathogens being the leading cause of economic losses. In the summer of 2023, a disease outbreak in hybrid catfish occurred on a commercial farm in South Texas, leading to significant fish deaths and economic losses. The affected fish were large and near market size. Early signs of the disease included reduced feeding, lethargy, and loss of balance. Laboratory analysis identified the pathogen Plesiomonas shigelloides, a bacterium known to cause gastroenteritis in humans and animals. This bacterium was found to be resistant to multiple FDA-approved antibiotics used in U.S. aquaculture, making treatment difficult. The findings highlight P. shigelloides as a growing threat in U.S. catfish farming, especially under high-density, intensive production systems where diseases can spread more easily, and emphasize the need for improved disease management practices, such as better biosecurity, vaccination, and water quality management.

Technical Abstract: During the summer of 2023, a spontaneous disease outbreak occurred in intensively stocked hybrid catfish (' channel catfish, Ictalurus punctatus × ' blue catfish, I. furcatus) in earthen ponds on a commercial aquaculture farm in South Texas. The farmer reported 50 to 80 dead fish per pond daily for a month. The fish were market size (1.0 ± 0.3 kg on average), resulting in substantial economic losses. Fifteen moribund fish were submitted for laboratory examination. Grossly, the fish showed distended abdomens, erythematous fins, and inflamed vents. Autopsy demonstrated visceral congestion, distended gastrointestinal tracts, and serosanguineous peritoneal effusion. Bacterial cultures from the internal organs revealed homogeneous bacterial growth after incubation. Presumptive biochemical characterization of the isolated bacteria identified Plesiomonas shigelloides. Further molecular confirmation was achieved by species-specific PCR amplification and 16S-rRNA sequencing. Juvenile catfish were experimentally challenged with the recovered isolates to fulfill Koch’s postulates. Moreover, an antibiogram was performed to evaluate the susceptibility of the isolates to a panel of FDA-approved antimicrobials. P. shigelloides isolates were pathogenic to channel catfish and alarmingly multidrug-resistant. We report here, for the first time, P. shigelloides infection in Texas commercial catfish aquaculture, emphasizing its significance as an emerging enteric pathogen that is difficult to treat with FDA-approved antimicrobials.