SIMS

Oyster Image
Photo: Photography Unit, Macquarie University
© Photography Unit, Macquarie University

The parasite was first detected in Queensland in the early 1970s and spread rapidly throughout that State's waterways, into rivers in northern NSW, and finally to Sydney. It has seriously affected oyster production in all these areas, with production in the Georges River for example, decreasing from 1,100,000 dozen oysters in 1993/94 to 62,000 dozen oysters in 2000/01.

"We've discovered that the defensive system in oysters from QX prone areas is suppressed before disease outbreaks occur," explains Raftos. "It may be that in other places the parasite is always present in oysters but is normally kept in check by the oyster's defensive systems. It seems that it's only when an oyster's defences are knocked down that the parasite can spread through that oyster and kill it."

The positive news for oyster producers is that some oysters may actually be demonstrating a resistance to the parasite's deadly effects. This phenomenon has allowed NSW Fisheries to start breeding programs with the aim of producing QX resistant oysters.

"There is a possibility that the Sydney rock oyster industry will be marginalised if we don't solve the mysteries of this parasite, but I am confident that intensive, focused research of the type we're doing will find the answers before that can happen," Raftos says.