Cultured eel (Anguilla bicolor) represents an economically significant aquaculture commodity; however, bacterial infections continue to pose a major challenge by reducing fish health and production performance. The objective of this study was to detect and identify pathogenic bacteria isolated from cultured eels in Notog Village, Patikraja District, Banyumas Regency, Indonesia, through molecular analysis targeting the 16S rRNA gene. Twenty eel samples were collected from a single culture pond, and bacterial isolates were obtained from liver tissues. The isolates were cultured on Tryptone Soya Agar (TSA) and subsequently observed on Glutamate Starch Phenol (GSP) medium. Genomic DNA was extracted from bacterial cultures and amplified using universal bacterial primers 27F and 1492R. PCR products were visualized by agarose gel electrophoresis, sequenced, and analyzed using BLAST against the GenBank database. Phylogenetic relationships were reconstructed using the Neighbor-Joining method with 1000 bootstrap replications in MEGA 12. PCR amplification produced clear DNA bands of approximately 1500 bp in both isolates, consistent with the expected size of the nearly full-length bacterial 16S rRNA gene. BLAST analysis indicated that isolate 1.4.3 exhibited the highest similarity to Aeromonas dhakensis (97.19%), while isolate 4.4.3 showed the highest similarity to Aeromonas veronii (96.86%). Phylogenetic analysis confirmed that both isolates clustered within the Aeromonas clade and were distinctly separated from the outgroup Streptococcus agalactiae. These results demonstrate that pathogenic Aeromonas species are associated with cultured eels in the study area. The findings underscore the importance of molecular surveillance, water quality management, and biosecurity measures to prevent bacterial disease outbreaks in eel aquaculture.
