Sentinels in the bay: using farm fish to monitor for pathogens in the environment

The objective of this study was to use sentinel fish to determine whether fallowing would effectively reduce the Infectious haematopoietic necrosis (IHN) load around sites in an area where every mariculture site had a history of IHN. The approach involved re-introducing fish to a few strategically placed (sentinel) sites and monitoring them for the presence of the virus over a specified period. Eighteen site visits and 217 viral plaque assays were carried out. No IHN virus was detected in the morts collected during the site visits, nor were there any positive reports from the passive surveillance system. Blood samples collected at the end of the grow-out period, indicated that the fish from one of tha sites had antibodies to IHN virus at the tome of harvest. Infectious haematopoietic necrosis virus was detected on this site ten months after fish were transferred to the site.