Since the advent of barramundi, Lates calcarifer Bloch, farming in Thailand in the early 19702, major problems have been encountered with the survival of larvae under hatchery conditions. Mortality rates of 50-90% are common during the first few weeks of life with an average survival rate of 20-30%. A similar situation exists in Malaysai (Awang 1987) and nothern Australia (Mackinnon 1987), where a number of theories have been advanced as to the possible cause of the disease. Clinical signs included lethargy, anorexia, pale-grey colouration and swimming in a darting or corkscrew fashion.
Watanabe, Kitajima & Fujita (1983) postulated that a dietary deficiency of highly unsaturated fatty acids was responsible and this was leter supported by Rodgers & Barlow (1987). It has also been suggested that high levels of undissociated ammonia may have caused extensive vacuolation in the brains of 12-14 day-old larvae (J.D. Humphrey & J.R. Langdon, personal communication).
This paper reports the discovery of a picorna-like virus in degenerative areas of the brain and retina in 15-, 17- and 18-day-old larvae from a hatchery in North Queensland.