Immunological Prevention of an Emerging Red Sea Bream Iridovirus [RSIV] in Cage-Cultured Spotted Mandarin Siniperca Scherzeri in Dandong, Northeast China

Red sea bream iridovirus [RSIV] is one of the most important causative agents in marine finfish industry, and RSIV was documented rarely in freshwater fish. Here, a novel RSIV, designated as Megalocyti-KD1201, was isolated and characterized from a natural mass mortality of cage-cultured spotted mandarin S. Scherzeri, one of the seven fish species in genus Siniperca, in Dandong, Northeast China. By phylogenetic analysis, Megalocyti-KD1201 was classified into a distinct RSIV clade, in which clade an early well-known genome-sequenced RSIV-Ehime-1 isolate in Japan was included. Vaccination trials showed that inactivated whole cell vaccines [Megalocyti-KD1201 strain] conferred effective protection to vaccinated spotted mandarin, and greater than 90% protection were obtained in two field tests in cage-cultured spotted mandarin during 2016- 2018. By contrast, less than 15% survivals were obtained in non-vaccination group. Vaccine inoculation showed a highly efficient treatment to prevent natural outbreak of RSIV diseases in cultured spotted mandarin.