VIRAL DISEASES OF FISH AND SHELLFISH IN AUSTRALIAN MARICULTURE

Except for table and pearl oyster culture, marine aquaculture in Austr alia has only a short history. This, together with the less intensive culture methods which are usually employed, probably explains why rela tively few viral diseases have been detected and even fewer are of sig nificance, However, we predict that, as more species are brought into aquaculture and management practices intensify, viral diseases of both fin- and shellfish will assume greater significance. The one exceptio n is salmonid mariculture which is based on stocks which are uniquely free of the major, pathogenic salmonid viruses as a result of their ef fective quarantine from northern hemisphere populations. In Australian finfish mariculture the major pathogen is the nodavims which causes m ass mortality in larval barmmundi (Lates calcarifer). The recent massi ve mortality of pilchards (Sardinops sagax) is also discussed as are l ymphocystis and a number of less important viral diseases. No viruses of commercial significance have been detected in Australian molluscs; although a herpesvirus infecting juvenile clams Katelysia sp. has been a significant impediment to commercialisation of these shellfish. The situation with shrimps is somewhat different as a new syndrome called mid-crop mortality syndrome (MCMS) has caused major losses. This synd rome appears to be a multifactorial disease with at least four viruses being visualised by electronmicoscopy. Of these, two are regarded as the most important; a parvo-like virus (spawner-isolated mortality vir us) and a possible rhabdo-like virus (gill-associated virus) which res embles yellowhead virus.