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

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.

Simple and cost-effective SNP genotyping method for discriminating subpopulations of the fish pathogen, Nocardia seriolae

“…N. seriolae infections have a significant impact on fish farming and food security in Asia, with nocardiosis outbreaks continuing to result in large economic losses due to mass fish mortalities (Labrie et al, 2008, Maekawa et al, 2018, Lei et al, 2020, Liao et al, 2021. Conventional N. seriolae genotyping methods e.g.…”

Screening and evaluating honokiol from Magnolia officinalis against Nocardia seriolae infection in largemouth bass (Micropterus Salmoides)

“…It is a chronic disease that usually lacks observable signs in fish during the early infection, but outbreak occurs in the mid‐phase of the culture cycle, at which point it is difficult to cure and thus resulting in severe economic losses to breeders (Elkesh et al, 2013; (Wang et al, 2007); Wang et al, 2009). The causative agent of nocardiosis is the gram‐positive, aerobic, filamentous bacterium Nocardia spp., of which Nocardia seriolae is the most frequent species (Hoang et al, 2020; Lei et al, 2020). Since the first case of N. seriolae infection reported in seabass in 2000, more than 20 freshwater and marine fish species have been found to be susceptible to this pathogen (Chen et al, 2000; Huang et al, 2021).…”

“…Since the first case of N. seriolae infection reported in seabass in 2000, more than 20 freshwater and marine fish species have been found to be susceptible to this pathogen (Chen et al, 2000; Huang et al, 2021). At present, N. seriolae has become a primary pathogenic bacterium in aquaculture, posing an increasing threat to aquaculture industry, especially in Asia (Huang et al, 2021; Lei et al, 2020; Wang et al, 2009). Current therapeutic means rely mainly on a limited number of antibiotics; however, prolonged and extensive administration may trigger a series of serious problems, such as environmental contamination, drug residues and a rise in drug resistance (Hoang et al, 2020; Maekawa et al, 2018).…”

“…Since its introduction to China in the 1980s, the production has been continuously increasing and has become a commercially important cultured fish in China (Huang et al, 2021). However, nocardiosis caused by N. seriolae poses a great threat to the largemouth bass aquaculture industry (Hoang et al, 2020; Huang et al, 2021; Lei et al, 2020). In this study, 80 medicinal plants were selected as candidates, and the antibacterial activity of their crude extracts was evaluated using a modified microplate resazurin assay method.…”

Responses of largemouth bass ( Micropterus salmoides , Lacépède, 1802) to fishmeal‐, and fish oil‐free diets

“…However, several issues presently hinder the future expansion of LMB production in China and elsewhere. For example, the emergence of various viral and bacterial diseases has taken their toll on production (Gui & Zhang, 2018; Lei et al, 2020; Xia et al, 2018). The lack of genetically improved strains, and poor seed quality, production and distribution, have likewise been recognized as obstructive to industry growth (Bai & Li, 2018; Hussein et al, 2020).…”