MASS MORTALITY OF CULTURED SEVENBAND GROUPER, EPINEPHELUS-SEPTEMFASCIATUS, ASSOCIATED WITH VIRAL NERVOUS NECROSIS

Mass mortalities of sevenband grouper Epinephelus septemfasciatus rear ed in Oita Prefecture were investigated. The outbreaks of the disease occurred in summer seasons (July to October; water temperature 25-28 d egrees C) of 1993 and 1994. Affected fish ranging 170 to 1,850g in bod y weight were characterized by upside down swimming and inflation of s wimbladder. Histopathologically, necrosis and vacuolation in the centr al nervous tissues and retina were observed. Although bacteria or para sites associated with the disease were not detected from affected fish and no CPE was observed on RTG-2, BF-2, and EPC cell lines, spherical virus particles, 28 nm in diameter, were found abundantly in the cyto plasm of affected nerve cells of most of the affected fish. The virus was identified as a fish nodavirus (nervous necrosis virus), based on the results of fluorescent antibody technique test with anti-SJNNV rab bit serum and polymerase chain reaction test with primers for amplific ation of SJNNV coat protein gene. These results suggest that the morta lities of sevenband grouper were at least partly due to viral nervous necrosis (VNN). This is the first report describing VNN of sevenband g rouper and the first case of VNN in the adult fish.