Development of a Highly Permissive Mandarin Fish () Kidney Cell Line for Mandarin Fish Ranavirus Using a Single-Cell Cloning Method.

Mandarin fish ranavirus (MRV) infection poses a substantial challenge to the mandarin fish culture industry as no effective preventive or therapeutic measures currently exist. The creation of a highly permissive cell line from a natural host is crucial for developing a vaccine for MRV and understanding its pathogenic mechanisms. In this research, the mandarin fish () kidney cell line (SCK) was isolated from mandarin fish kidneys. Subsequently, SCK-a to SCK-g monoclonal cell lines were derived from the SCK cell population, distinguished by morphological variations. Notably, MRV infection induced an advanced cytopathic effect (CPE) in almost all cells of the SCK-f clone. Further tests showed that MRV achieved a peak viral titer of 10 50% tissue culture infectious dose (TCID)/mL and consistently exceeded 10 TCID/mL across nine passages in SCK-f cells. Electron microscopy verified the MRV virion integrity within SCK-f. In vivo experiments revealed that MRV infections led to cumulative mortality rates of 86.9% in mandarin fish and 88.9% in largemouth bass (). Such results suggest that SCK-f is highly permissive to MRV. This study underscores the importance of cellular diversity in developing viral permissive cell lines. The SCK monoclonal cell line pool may offer potential for generating highly permissive cell lines for other mandarin fish viruses.