Nodavirus infection of juvenile white seabass, Atractoscion nobilis, cultured in southern California: first record of viral nervous necrosis (VNN) inNorth America

The viral aetiology of mass mortalities of white seabass, Atractoscion nobi lis, cultured in southern California, USA was examined. Disease outbreaks o ccurred in juvenile fish reared at two culture facilities from lune to Dece mber 1999, with clinical signs such as anorexia and erratic swimming motion . Microscopic lesions observed in moribund fish included marked vacuolation of brain, spinal cord and retina. The piscine nodavirus (Betanodavirus), t he causative agent of viral nervous necrosis (VNN), was detected in the aff ected tissues by electron microscopy, indirect fluorescent antibody test (I FAT), reverse transcription-polymerase chain reaction (RT-PCR), and isolati on in cell culture. The agent was identified as one of the four known genot ypes of piscine nodavirus. In addition, a similar nodavirus was also detect ed in fish samples from disease outbreaks at the same facility in 1992. In the last decade, VNN has been report ed among cultured populations of marin e fish worldwide and this paper is the first record of the agent in North A merica.