Dynamics of infectious salmon anemia virus in biofouling on well-boat hulls

Infectious Salmon Anemia Virus (ISAV) is a significant pathogen in the aquaculture industry worldwide, posing serious threats to fish health and causing substantial economic losses for producers. Thus, understanding potential transmission pathways and implementing strategies to reduce the spread of infection between production sites is crucial. This study investigated the dynamics of ISAV RNA in biofilms on internal surfaces and in external hull biofouling of wellboats during fish transfer operations from ISAV-infected sites. Sampling was conducted at six defined phases of the transport process, including before and after cleaning, disinfection, and fallowing. Results revealed the presence of ISAV RNA in internal biofilms and external biofouling of wellboats. Virus loads were highest in fish mucosal samples during transport, with lower but detectable levels in exterior hull biofouling, internal surface biofilms, and water samples. Thorough cleaning, disinfection, and a 48-h fallowing period yielded no detection of ISAV RNA on tested surfaces. However, while these procedures are routinely performed after all fish have been transferred from the site, they are not applied between multiple delivery trips usually required for transfers. Our findings emphasize the role of exterior hull biofouling as a potential reservoir for ISAV particles and highlight the importance of stringent biosecurity protocols for preventing pathogen transmission in aquaculture. Nevertheless, since this study detected ISAV RNA rather than viable virus, future work will be needed to confirm whether detected viral RNA in hull biofouling represents infectious particles capable of transmission.