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Diseases of Aquatic Organisms

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DAO 149:33-45 (2022)  -  DOI: https://doi.org/10.3354/dao03659

Isolation, identification, and pathogenic characteristics of Nocardia seriolae in largemouth bass Micropterus salmoides

Zhi-Gang Liu1,2, Jun-Jian Dong1,2, Xiao-Li Ke1,2, Meng-Meng Yi1,2, Jian-Meng Cao1,2, Feng-Ying Gao1,2, Miao Wang1,2, Xing Ye1,2, Mai-Xin Lu1,2,*

1Key Laboratory of Tropical and Subtropical Fishery Resource Application and Cultivation, Ministry of Agriculture and Rural Affairs, Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, PR China
2Guangdong Provincial Key Laboratory of Aquatic Animal Immune Technology, Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou 510380, PR China
*Corresponding author:

ABSTRACT: The largemouth bass Micropterus salmoides is an important freshwater aquaculture fish in China. Recently, largemouth bass at a fish farm in Guangdong province experienced an outbreak of a serious ulcer disease. As part of the investigations conducted to identify the aetiology and identify potentially effective control measures, we isolated a pathogenic bacterium (NK-1 strain) from the diseased fish. It was identified as Nocardia seriolae through morphological observation, physiological and biochemical analysis, and molecular identification, and its pathogenicity was verified by experimental infection. Pathological changes in the diseased fish included granulomatous lesions in the liver and spleen, destruction of renal tubules, necrosis of intestinal epithelial cells, infiltration of inflammatory cells in the brain, vacuolation of cells, and swelling and cracking of the mitochondria and endoplasmic reticulum. Bacterial detection using qPCR showed that the spleen and intestine were the main organs targeted by N. seriolae. The mortality of largemouth bass experimentally infected with N. seriolae at 21°C was significantly lower than that in fish infected at higher temperatures between 24 and 33°C; there were no significant differences in the levels of mortality at these higher temperatures. The level of mortality of largemouth bass infected with N. seriolae was lowest at a neutral water pH of 7 but increased significantly at higher and lower pH. Of the tested Chinese herbal medicines, Chinese sumac Galla chinensis and Chinese skullcap Scutellaria baicalensis exhibited the best antibacterial effects. This study lays a foundation for the clinical diagnosis and scientific control of ulcer disease in largemouth bass.


KEY WORDS: Largemouth bass · Micropterus salmoides · Nocardia seriolae · Ulcerative lesions · Nodular lesions · Pathogenic characteristics


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Cite this article as: Liu ZG, Dong JJ, Ke XL, Yi MM and others (2022) Isolation, identification, and pathogenic characteristics of Nocardia seriolae in largemouth bass Micropterus salmoides. Dis Aquat Org 149:33-45. https://doi.org/10.3354/dao03659

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