A mystery illness which continues to plague Port Stephen's multimillion dollar Pacific oyster crops, has growers and biosecurity experts stumped.
Hundreds of thousands of oysters have died since late last year, raising fears the port may need to be quarantined to curtail further spread of the disease.
Twenty batches of affected oysters have been tested for the virus which causes Pacific Oyster Mortality Syndrome, however all returned negative results.
Environmental factors are currently being investigated.
