In both cultured and wild ponds, nocardiosis is a chronic, systemic disease with a long survival time from natural infection to death in fish Our previous results showed that N. seriolae colonized visceral tissues and caused the formation of granulomas within the snakehead tissues at 3–4 d post-challenge under artificial challenge conditions (data not published). Therefore, we believe that sampling at 96 h (4 days) post-challenge might be more advantageous for analyzing mechanisms of the host–N. seriolae interaction in snakeheads. .