Viral Disease Histopathology in Aquaculture Finfish: Organ‐Specific Pathological Changes and Diagnostic Insights, Referencing the World Organisation for Animal Health: A Review

ABSTRACT The aquaculture industry faces significant challenges from viral diseases, many of which are listed by the World Organisation for Animal Health (WOAH) as priority pathogens due to their impact on global finfish health and production. This review synthesizes current knowledge on the histopathology of key WOAH‐listed viral pathogens, including Koi Herpesvirus (KHV), Infectious Salmon Anaemia Virus (ISAV), Viral Hemorrhagic Septicemia Virus (VHSV), Megalocytivirus, Infectious Hematopoietic Necrosis Virus (IHNV), Spring Viremia of Carp Virus (SVCV), Salmonid Alphavirus (SAV), Tilapia Lake Virus (TiLV), and Epizootic Hematopoietic Necrosis Virus (EHNV). We provide a detailed examination of organ‐specific lesions, emphasizing spleen, kidney, gill, and gut pathology across diverse host species. Despite an expanding literature, important gaps persist, including inconsistent lesion scoring methods, limited comparative histopathological analysis across species, and underutilization of integrated molecular and histological diagnostics. Addressing these gaps through harmonized scoring systems and integrative diagnostic approaches is critical for improving disease diagnosis, control strategies, and sustaining aquaculture productivity worldwide. This review serves as a comprehensive resource to inform future research and health management practices related to viral diseases in aquaculture finfish.