Nocardia seriolae infection in the cultured eel Anguilla japonica in Korea

Abstract

Mass mortality occurred at an Anguilla japonica eel farm equipped with a recirculating aquaculture system in Gimcheon, Korea, from late spring to early summer 2015. The cumulative 3-month mortality was 16% (approximately 24,300-150,000 fish). The majority of affected fish displayed ulcerative lesions that progressed to petechial haemorrhages and small white granulomas in the major organs. A Gram-positive, acid-fast, nonmotile bacterium was isolated from internal organ lesions. Phylogenetic analysis of 16S rRNA identified the species as Nocardia seriolae and the strain was designated EM150506. Afterwards, naïve eels were injected with 1.8 × 10 colony-forming units per fish to confirm the strain's pathogenicity, which resulted in a 20% mortality rate within 4 weeks. However, surviving fish still exhibited white N. seriolae colonies in internal organs. To our knowledge, this is the first report of a N. seriolae infection in cultured eel.

Isolation and characterization of Nocardia seriolae , a causative agent of systematic granuloma in cultured East Asian four finger threadfin, Eleutheronema rhadinum, and red snapper, Lutjanus erythropterus

“…East Asian four finger threadfin presented with more acute lesions with necrosis and suppurative fluid present under the lesion. This phenomenon also occurred on cultured eel, A. japonica (Kim et al., 2018). N. seriolae causes illness in fish and possesses several intracellular virulence factors (tyrosine phosphatase A, protein tyrosine phosphatase B, antigen 85 (Ag85), and TlyA protein) and produces an extracellular product (histone‐like DNA‐binding protein), which can cause immune depression, haemolysis and can induce disease in fish (Wang et al., 2019; Yasuike et al., 2017).…”

“…Nocardia seriolae is a Gram‐positive and non‐motile bacterium that primarily infects marine fish in Asian countries such as Japan, Malaysia, Taiwan, Indonesia, Vietnam, Korea and China. Fish that have been infected by N. seriolae include Japanese flounder ( Paralichthys olivaceus ) (Kudo et al., 1988), sea bass ( Lateolabrax japonicus ) (Chen et al., 2001), large yellow croaker ( Larimichthys crocea ) (Wang et al., 2005), meagre ( Argyrosomus regius ) (Elkesh et al., 2012), pompano ( Trachinotus blochii ) (Vu‐Khac et al., 2016), jade perch ( Scortum barcoo ) (Wang et al., 2017a), eel ( Anguilla japonica ) (Kim et al., 2018) and orange‐spotted grouper ( Epinephelus coioides ) (Nguyen et al., 2019). Diseased fish are commonly found to exhibit yellow or whitish nodules, which are indicative of granulomas in the internal organs, especially the spleen, liver, and kidney.…”

“…Overall, nocardiosis will only cause low levels of chronic mortality in fish culture (Labrie et al., 2008). However, these infections cause huge economic loss owing to high cumulative mortality, for example, N. seriolae caused 30%–35% cumulative mortality within 1 month in snakehead fish ( Ophiocephalus argus ) in China (Wang et al., 2007) and a cumulative 3‐month mortality of 16% in the eel A. japonica in Korea (Kim et al., 2018).…”

Molecular Identification of Nocardia seriolae and Comparative Analysis of Spleen Transcriptomes of Hybrid Snakehead (Channa maculata Female × Channa argus Male) With Nocardiosis Disease

“…are filamentous and Gram-positive bacteria found in nature as soil saprophytes (6). They are opportunistic pathogens, and some species are pathogenic to fish (7)(8)(9). Fish nocardiosis is a systemic disease with the main clinical symptoms of skin ulceration and granuloma formation of internal organs (6).…”

Comparative genomics of Nocardia seriolae reveals recent importation and subsequent widespread dissemination in mariculture farms in South Central Coast, Vietnam

“…Nocardiosis has also impacted several other important fish species within the Japanese aquaculture industry such as amberjack ( Seriola dumerili ), Japanese flounder ( Paralichthys olivaceus ), and chub mackerel ( Scomber japonicas ) . N. seriolae has subsequently been documented in Taiwan, China, Korea, USA, and Mexico, where high mortalities and associated economic losses due to nocardiosis having been reported in freshwater and marine fish species in both cultured and wild populations (Kudo et al, 1988, Chen et al, 1989, Chen and Tung, 1991, Chen et al, 2000, Huang, 2004, Park et al, 2005, Shimahara et al, 2008, Shimahara et al, 2009, Cornwell et al, 2011, Kim et al, 2018, Del Rio-Rodriguez RE, 2021). Despite causing significant economic losses in fish aquaculture worldwide, there are currently no effective measures against nocardiosis.…”