en fish disease fish disease پژوهشي Orginal research papers <em>Aeromonas hydrophila </em>is an opportunistic pathogen causing high mortality and economic burden in freshwater fish farming. This study aims to develop a co-agglutination method for detecting and creating <em>Aeromonas hydrophila </em>diagnostic rapidly. In this study, we injected rabbits (&plusmn;2kg weight) with 1mL of <em>A. hydrophila</em> antigen suspension 1.2 x 10⁹cfu mL^&ndash;1 at one week intervals (three times, intra vena) respectively. The gouramis (15.48&plusmn;0.55g-1 weight) were infected by <em>Aeromonas hydrophila, Aeromonas sobria</em>, <em>Aeromonas salmonicida</em>, <em>Streptococcus agalactiae</em>, and <em>Pseudomonas aeruginosa</em> separately with 0.1 mL fish^&ndash;1 and 10⁸ cfu mL^&ndash;1 bacterial cell suspensions. The antiserum was purified to couple with the <em>Staphylococcus aureus </em>suspension protein A, in a 1:1 (v/v) ratio and used by the co-agglutination reagent. We compared this method with standard polymerase chain reaction (PCR) for <em>A. hydrophila </em>detection. The rabbit antibody reaction occurred only against <em>A. hydrophila </em>antigen showing specificity of the gourami tissue supernatant within 10-30 seconds. The sensitivity test had a detection limit of 10⁶ cfu mL^&ndash;1. Comparison detection method with PCR showed that positive result of <em>A. hydrophila </em>was located in 209 bp. Co-agglutination method could detect <em>A. hydrophila </em>in the internal organ of fish at 12h after injection, but the PCR method could detect at one hour after injection. This research concluded that co-agglutination method could detect <em>A. hydrophila </em>specifically, sensitively, rapidly and practically in laboratory and field examination. Aeromonas hydrophila, Diagnostic, Rapid, Co-agglutination Method. 141 156 http://jifro.ir/browse.php?a_code=A-10-3103-1&slc_lang=en&sid=1 M. Dian Fitria dianfitria.manurung@gmail.com 100319475328460039194 100319475328460039194 No Bogor Agricultural University S. Sukenda sukenda@ipb.ac.id 100319475328460039195 100319475328460039195 Yes Bogor Agricultural University M. Yuhana yuhanamunti@gmail.com 100319475328460039196 100319475328460039196 No Bogor Agricultural University