Since 1986, an unknown disease causing high mortalities appeared in Ifremer's Pacific OceanologicaI Center (Tahiti) nursery of sea bass (Lates calcarifer). opathology of lesions involving both centraI nervous system (CNS) and eye retina, and the tuation exists in South-East Asian countries (Indonesia, Philippines, Malaysia and Singapore), and in northem Australia. This paper describes the histmorphology of a new fish virus, which is believed to be the aetiological agent of high mortalities among sea bass larvae.