Koi herpesvirus disease causes mass mortality events in farmed and wild carp populations, with affected fish experiencing prolonged distress before death in poorly managed biosecurity systems.
Koi herpesvirus kills through gill damage that progressively impairs breathing, causing hypoxia over days. Affected fish show clear distress behaviors — gasping at the surface, abnormal swimming, and reduced feeding — that reflect the experience of gradual suffocation. Improved biosecurity and vaccination not only protect production but substantially reduce the welfare cost of disease outbreaks in both farmed and wild fish populations.