Identification and characterization of a new strain of Micropterus salmoides rhabdovirus (MSRV-Bces-Ts23) isolated from greenfin horse-faced filefish (Thamnaconus modestus) in China

Micropterus salmoides rhabdovirus (MSRV) is a pathogenic rhabdovirus previously known to infect the freshwater fish largemouth bass ( Micropterus salmoides ), causing high mortality and significant economic losses in aquaculture. However, MSRV infection in marine fish remains unreported. This study reported the first identification and characterization of a novel MSRV strain, termed MSRV-Bces-Ts23, isolated from diseased juvenile greenfin horse-faced filefish ( Thamnaconus modestus ) in northern China. Numerous diagnostic approaches, including transmission electron microscopy, RT-PCR, metavirome sequencing, and genome assembly, confirmed the viral identity. It caused typical cytopathic effects and showed high sequence similarity to previously reported MSRV strains. The complete genome of MSRV-Bces-Ts23 was 11,567 bp in length and encoded five structural proteins (N, P, M, G, and L). Phylogenetic analysis indicated that MSRV-Bces-Ts23 clustered within the MSRV lineage and was closely related to known strains. Additionally, virions and pathological lesions were detected in the brains of greenfin horse-faced filefish following intraperitoneal infection with the virus. Moreover, an absolute quantification standard curve targeting the G gene and fourteen potential B-cell epitopes of the G protein were identified, contributing to accurate viral detection and providing promising targets for immunological control. In conclusion, our findings revealed the potential for host range expansion of MSRV and emphasized the urgency of broad monitoring and prevention in various cultured fish. • First identification of MSRV in marine fish T. modestus . • MSRV-Bces-Ts23 genome (11,567 bp) encodes five structural proteins. • Standard curve for MSRV-Bces-Ts23 G gene enables precise viral quantification. • Brain of T. modestus is the main target of MSRV-Bces-Ts23 infection.