Fletcher et al. (1997) suggest that the size of the outbreak in 1995 are consistent with infection of a naïve Australian pilchard population by an exotic herpes virus to which they had never previously been exposed. The use of imported pilchards to feed caged southern bluefin tuna in South Australian waters provides a potential source of such a virus. This is one explanation that highlights the need for a panel of diagnostic reagents and tests to screen imported pilchards for the presence of the herpes virus.

Herpes viruses are well-known to cause latent infections whose existence remains unknown until a predisposing environmental factor leads to their recrudescence. The factor most commonly recognised in virus reactivation is stress tha tcan itself be induced by a variety of stimuli including infection by another, unrelated microorganism. Fletcher et al. (1997) suggest that the severity of the disease observed in Australian pilchards and its emanation from a single geographic locality are not consistent with reactivation of a latent infection. However, we can not at this time rule out the possibility that the herpes virus is endemic and present in a latent state in Australian pilchards and is activated following infection by and, as yet, unidententified microorganism that spreads from a point source in South Australia. Imported pilchards may or may not be the source of such microorganism. There is a need to rule out involvement of other microorganisms in the death of the pilchards and to use the panel of diagnostic reagients and tools mentioned above to determine if Australian pilchards are latently infected by a herpes virus. Mortalities observed in the juvenile fish populuation in 1998 but not in 1995 raise questions about the role of herpes virus in the recent outbreak. There is a need to determine if herpes virus is present in dead juvenile fish.

Fletcher. W.J., Jones, B., Pearce, A.F. and Hosja (1997). Environmental and biological aspects of the mass mortality of pilchards (Autumn 1995) in Western Australia. Fisheries Research Report No 106, Fisheries Department of Western Australia.

Translocation of aquatic animals or products of aquatic animal origin is frequently identified as a key event that precedes major outbreaks of disease caused by pathogens that were previously unknown in that region or species (Stewart 1991, Durand et al. 2000). Introduced diseases in wild fisheries usually cannot be eradicated, and can have significant ongoing economic and ecological implications. A pathogen risk analysis is required to identify not only the types and quantities of bait being used in Australia, but also whether their translocation and use represents a significant threat to aquatic animal health at regional and national levels. The strategic benefits of the proposed project therefore will be to identify potential disease risks associated with domestic bait translocation, and rank the disease risks in order to provide information essential for policy development at a future date.