Abstract: Spotted scat Scatophagus argus is popularized in South China as a new resource of marine aquaculture and ornamental fish in recent years. The research of S. argus was focused on biological characteristics, gonad development and reproduction, composition of muscle, artificial culture and the construction of a cell line, and so on. Until now, only three parasites, including Lenolopa huizhouensis, Metahaliotrema mizellei and M. gemiratohamula have been recorded to exist in the gut and gill of S. argus. In aquaculture, priority is given only to bacterial diseases caused by various aquatic pathogenic bacteria, which led to enormous economic loss in the aquatic animals, but the bacteria diseases were not reported in the S. argus. Therefore, the tasks of comprehensive study on the bacterial disease in S. argus become more urgent and important. In order to separate and identify the pathogen of fulminant disease in S. argus cultured in a laboratory in Shanghai Ocean University, we used the traditional method of pathogen isolation, virus and parasite were not detected, but we obtained a bacterial strain isolated from the diseased fish liver. And then, we observed the isolate strain by the electron microscope and tested the physiological and biochemical identification, and histopathological analysis was made in the natural incidence of fish, in addition, artificial infection was also implemented according to Koch's postulates. The results show that the isolate is a Gram-negative staining, cells straight with rounded ends, 0.8-1.0 μm ×1.0-2.0 μm, while observed by electron microscope, and consistent with A. hydrophila through physiological and biochemical characteristics. 16S rRNA gene sequence analysis by Blast in GenBank indicates that the isolate (accession number:KR006248) showed high levels of similarity to Ah ATCC7966 (99%). A phylogenetic tree of the isolate and other Ah strains formed a tight cluster. Histopathological analysis of diseased fish shows the pathological damages, including gill lamellae cells denudation and leukocytes infiltration in gills, abscission of intestinal villus, muscles loosening in intestine and a marked increase of pyknosis of glomerulus in kidney, infiltrating of hemocytes and inflammatory cells in liver. The healthy S. argus could be infected through artificial infection using the isolated bacteria. The half of lethal dose (LD₅₀) to S. argus in 96 h is 7.35×10⁷ CFU/mL. To conclude, the Ah201416 strain was identified as A. hydrophila which is the pathogen for S. argus. This study provides a theoretical basis for disease control and prevention and calls on people to pay more attention to the potential dangers caused by A. hydrophila against S. argus.