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The bluegill sunfish, Lepomis macrochirus , is an important aquacultural and recreational species in southern China because of its excellent taste, rapid growth rate, and good looks. At present, few pathogens are known to affect the bluegill sunfish. However, an iridovirus-like disease recently caused heavy losses to the bluegill sunfish aquaculture industry in Guangdong, China. We report that a virus, designated BSMIV-SD-20171020, was isolated from diseased bluegill sunfish in China. The isolate was efficiently propagated in a Chinese perch brain (CPB) cell line. The cytopathic effect was observed, the MCP gene PCR amplified, and the virus observed with electron microscopy. Its viral titer in CPB cells reached 104.13 TCID 50 mL−1. The mortality rate was 100% when bluegill sunfish were challenged with BSMIV-SD-20171020 at a dose of 103.13 TCID 50 /fish. A histopathological examination revealed basophilic hypertrophied cells in the intestine, liver, and spleen. A nucleotide sequence alignment and phylogenetic analysis of the major capsid protein revealed that isolate BSMIV-SD-20171020 is the species Infectious spleen and kidney necrosis virus (ISKNV), in the genus Megalocytivirus. • The ISKNV-like virus BSMIV-22SD-20171020 was firstly isolated from diseased bluegill sunfish. • The isolate is belonging to genus Megalocytivirus genotype I by MCP genes sequences analysis. • The isolate was pathogenic to the bluegill sunfish, with 100% mortality after viral infection. [ABSTRACT FROM AUTHOR]

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°04′, N22°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 × 102 cfu/fish at 20 °C, but over 107 cfu/fish at 28 °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. • A. salmonicida could infect Chinese perch. • A. salmonicida caused hemorrhagic gill disease. • A. salmonicida in tropical climate. [ABSTRACT FROM AUTHOR]