Impact of Red Sea Bream Iridovirus Infection on Rock Bream (Oplegnathus fasciatus) and Other Fish Species: A Study of Horizontal Transmission

Simple Summary: Red sea bream iridovirus (RSIV) has been reported to be susceptible to various marine fish species in Asian countries such as South Korea, and it causes significant economic losses due to massive mortalities in rock bream (Oplegnathus fasciatus) in particular. However, studies on the impact of the virus shed from RSIV-infected rock bream on other fish species are limited. Here, we investigated the dynamics of the virus by simulating the natural conditions of RSIV infection in rock bream and examining its release into seawater and the risk of horizontal transmission through cohabitation with other fish species. Our data demonstrated that the virus shed from RSIV-infected rock bream caused high mortality rates in surrounding fish species through horizontal transmission. Our findings suggest the potential for RSIV-infected rock bream in farms to spread the disease to neighboring farms. Additionally, our results demonstrated a high correlation between RSIV load and viral shedding ratio in rock breams, as well as between RSIV load and histopathological infection grades. Red sea bream iridovirus (RSIV) causes significant economic losses in aquaculture. Here, we analyzed the pathogenicity, viral shedding, and transmission dynamics of RSIV in rock bream (Oplegnathus fasciatus) by employing immersion infection and cohabitation challenge models. Rock bream challenged by immersion exposure exhibited 100% mortality within 35 days post RSIV exposure, indicating that the viral shedding in seawater peaked after mortality. At 25 ffi C, a positive correlation between the viral loads within infected rock bream and virus shedding into the seawater was observed. Specific RSIV lesions were observed in the spleen and kidney of the infected rock bream, and the viral load in the spleen had the highest correlation with the histopathological grade. A cohabitation challenge mimicking the natural transmission conditions was performed to assess the virus transmission and determine the pathogenicity and viral load. The RSIV-infected rock breams (donors) were cohabited with uninfected rock bream, red sea bream (Pagrus major), and flathead grey mullet (Mugil cephalus) (recipients) at both 25 ffi C and 15 ffi C. In the cohabitation challenge group maintained at 15 ffiC, no mortality was observed across all experimental groups. However, RSIV was detected in both seawater and the recipient fish. Our results provide preliminary data for further epidemiological analyses and aid in the development of preventive measures and management of RSIVD in aquaculture.