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Diseases of Aquatic Organisms

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DAO 142:13-21 (2020)  -  DOI: https://doi.org/10.3354/dao03517

Nocardia seriolae: a serious threat to the largemouth bass Micropterus salmoides industry in Southwest China

Xueping Lei1, Ruoxuan Zhao1, Yi Geng1,*, Kaiyu Wang1, Ping Ou Yang1, Defang Chen2, Xiaoli Huang2, Zhicai Zuo1, Changliang He1, Zhengli Chen1, Chao Huang1, Hongrui Guo1, Weimin Lai1

1College of Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Sichuan 611130, PR China
2Department of Aquaculture, Sichuan Agricultural University, Wenjiang Sichuan 611130, PR China
*Corresponding author:

ABSTRACT: Nocardia seriolae is the causative agent of nocardiosis in both marine and freshwater fish. Here, we report on multiple outbreaks of nocardiosis associated with elevated mortality (23-35%) in farmed largemouth bass in Sichuan, China, from 2017 to 2018. A total of 9 strains isolated from diseased largemouth bass were identified as N. seriolae by phenotypic characterization, 16S rRNA and hsp65 gene sequence analysis. The clinical signs of infected largemouth bass included hemorrhage, skin ulcers and prominent tubercles varying in size in the gill, liver, spleen and kidney. Experimental infection indicated that these isolates were the pathogens responsible for the mortalities. In vitro antibacterial activities of 12 antibiotics against N. seriolae isolates were determined as minimum inhibitory concentrations. Histopathological observation of diseased fish infected with N. seriolae showed necrotizing granulomatous hepatitis, nephritis, splenitis, epithelial hypertrophy and hyperplasia with degenerative changes of the epithelium in the gill. Large quantities of bacterial aggregates were found in the necrotic area of the granuloma by Lillie-Twort Gram stain and immunocytochemistry. Our findings indicated that N. seriolae is a serious threat to the largemouth bass Micropterus salmoides industry in Southwest China.


KEY WORDS: Nocardia seriolae · Nocardiosis · Micropterus salmoides · Characterization · Outbreaks · Pathologic lesions · Aquaculture · Sichuan


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Cite this article as: Lei X, Zhao R, Geng Y, Wang K and others (2020) Nocardia seriolae: a serious threat to the largemouth bass Micropterus salmoides industry in Southwest China. Dis Aquat Org 142:13-21. https://doi.org/10.3354/dao03517

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