INVESTIGATION OF OUTBREAKS OF A NOVEL DISEASE, SLEEPY GROUPER DISEASE, AFFECTING THE BROWN-SPOTTED GROUPER, EPINEPHELUS-TAUVINA FORSKAL

A novel disease affecting the brown-spotted grouper, Epinephelus tauvina Forskal, described here as 'Sleepy Grouper Disease' (SGD), resulted in significant economic losses in some Singaporean marine net-cage farms from April to August 1992. Investigations suggested that the aetiological agent was a virus, probably introduced with imported groupers. The virus was provisionally identified as an iridovirus on morphological evidence. The disease caused extreme lethargy in affected fish with few visible external signs. Mortalities either occurred gradually over the week from onset of clinical signs, or over a shorter period and in large numbers if fish were stressed. Consistent tissue changes were seen by light microscopy in the spleen, heart and kidney of affected fish. Electron microscopy showed viral particles associated with damage to cell organelles. In an experimental infection, apparently healthy fish cohabiting with an infected fish developed similar lesions and died. The significance of SGD in grouper culture is discussed.