Epizootic mortalities in tilapia Oreochromis mossambicus

Periodic mortalities reaching 100% over a period of 60 d were observed in fry of tilapia Oreochromis mossambicus. Moribund fish exhibited rapid corkscrew-like swimming patterns ('spinning'), and the syndrome was successfully transmitted via cannibalism to naive populations of tilapia fry. Histology revealed no evidence of bacteria or parasites. Bohle iridovirus (BIV) infected tilapia and those succumbing to 'spinning tilapia' ('ST') syndrome shared similarities in histopathological lesions of kidney and muscle. Virus isolation in vitro from affected fish was unsuccessful. The barramundi Lates calcarifer bioassay indicated that the aetiological agent of the epizootic was BIV.