Hemorrhagic gill disease of Chinese perch caused by Aeromonas salmonicida subsp. salmonicida in China

Chinese perch (Siniperca chuatsi), is a major freshwater fish species of high economic value in the south of China. The disease is a major factor that restricts the development of Chinese perch aquaculture. In this study, we characterized a new pathogen in Chinese perch. In April 2018, the mortality of fish was measured in a Chinese perch farm (E113 degrees 04', N22 degrees 40') located in Jiangmen city, Guangdong province. The pathogen was identified as Aeromonas salmonicida subsp. salmonicida by biochemical characterization and molecular analysis. Experimental infection was carried out with healthy Chinese perch and showed that the 50% lethal dose (LD50) was 3.01 x 10(2) cfu/fish at 20 degrees C, but over 10(7) cfu/fish at 28 degrees C. These results suggest that A. salmonicida subsp. salmonicida was the causal agent of the losses observed in the Chinese perch farm, and temperature may be an essential factor for disease outbreak. This is the first report of A. salmonicida subsp. salmonicida in Chinese perch, also the first report of A. salmonicida-infected fish in a tropical region. A. salmonicida is usually considered a cold-water fish pathogen; however, our results show that it can also infect warm water fish species in tropical climates in south China. Greater attention should be paid to the epidemiology and prevention of A. salmonicida in warm water fish, especially in winter.