en fish disease fish disease پژوهشي Orginal research papers <em>Procambarus clarkii</em> crayfish has been developed as an excellent animal model to study the characteristics and pathogenesis of white spot syndrome virus and the host defense mechanisms of crustacean. However, due to pathogen infections of crayfish in Chinese farms, research based on this model has been slowed down.&nbsp;Using triplex polymerase chain reaction, we found the virulence <em>Aeromonas hydrophila</em> was one reason that caused the death of crayfish. The isolated AH-3 produced 100% mortalities with 3-24h after inoculation of 1&times;10⁶ colony-forming units of live cells per crayfish at 20 ˚C. White spot syndrome virus, Aeromonas hydrophila, Procambarus clarkii, Triplex polymerase chain reaction 1770 1779 http://jifro.ir/browse.php?a_code=A-10-1579-1&slc_lang=en&sid=1 Y. Zeng zy110cn@aliyun.com 100319475328460035541 100319475328460035541 Yes College of Life Sciences, Yantai University, Shandong, PR China