Eighty-one tetracycline-resistant Aeromonas sp. strains were isolated from farm-raised catfish. Morphological and biochemical characteristics indicated that 23 of the 81 aeromonads were Aeromonas hydrophila, 7 isolates were Aeromonas trota, 6 isolates were Aeromonas caviae, 42 isolates were Aeromonas veronii, and 3 isolates were Aeromonas jandaei. However, the AluI and MboI restriction fragment length polymorphism (RFLP) patterns of the PCR-amplified 1.4-kb 16S rRNA gene from all 81 tetracycline-resistant aeromonads from catfish were identical to the RFLP banding patterns of A. veronii ATCC 35626, indicating that all 81 isolates were strains of A. veronii. A multiplex PCR assay successfully amplified the 5 tetracycline-resistant genes (tetA to E) from the genomic DNA of all 81 isolates. The assay determined that tetE was the dominant gene occurring in 73/81 (90.0%) of the aeromonads. Plasmids (2.0 to 20 kb) were isolated from 33 of the 81 isolates. Dendrogram analysis of the SpeI pulsed-field gel electrophoresis identified 15 distinct macrorestriction patterns among the isolates. Our results indicate the need for use of 16S rRNA in the identification of Aeromonas spp. and the prevalence of catfish as a reservoir of tet genes.The United States produces more than $500 million per annum of pond-raised channel catfish (Ictalurus punctatus), primarily in the southeastern part of the country (4). Infectious diseases reduce catfish production by nearly 10% every year. Motile aeromonad septicemia, caused by Aeromonas hydrophila, is one of the common diseases accounting for the reduced production (5). Antimicrobials agents, such as oxytetracycline and Romet 30 (sulfadimethoxine-ormetoprim), are used to prevent the outbreak of infectious diseases (5, 32). However, widespread use of drugs may result in the selection of tetracycline-and sulfonamide-resistant bacteria in the aquaculture environment and may play a role in the dissemination of antibiotic resistance genes to clinical aeromonad strains (20,22).Aeromonads have been implicated in the cause of numerous human infections, such as gastroenteritis, cellulitis, meningitis, bacteremia, soft-tissue infections, peritonitis, and bronchopulmonary infections (8,15,(18)(19). Direct contact with contaminated water and soil is the most frequent cause of gastrointestinal and wound infections in humans (15). Broad-spectrum antibiotics, such as tetracycline, are prescribed clinically for the treatment of such infections.The molecular epidemiology of tetracycline-resistant aeromonads, especially Aeromonas salmonicida, has been well documented (2,3,29). These studies indicate that tetracycline resistance is plasmid-encoded and that, among the different classes of tetracycline-resistant genes, tetA is predominant. Schmidt et al. (29) reported the isolation and characterization of oxytetracycline-sulfonamide/trimethoprim-resistant aeromonads from Danish rainbow trout farms. Their PCR data indicate tetE as the predominant determinant, followed by tetA and tetD. Earlier, DePaola et al. ...