Sampling work in Foveaux Strait has not uncovered any further cases of the deadly oyster parasite, Bonamia ostreae.
A biosecurity response was launched in March after three wild oysters were found to be infected. While the parasite does not pose any food safety risk, it can kill flat oysters, putting the entire Bluff oyster trade at risk.
In recent weeks scientists at Niwa have been testing more than 2000 oysters taken from 15 sites in the Foveaux Strait, to better understand the possible extent of the recent discovery.
Biosecurity New Zealand spokesperson Dr Catherine Duthie said all the results had been negative.
Duthie said the sampling programme had been designed to detect infection down to levels of 2 percent of the Foveaux Strait oyster fishery and the results indicated the disease was likely in very low prevalence.
"It's good news that we didn't find anything further ... what that means for the programme is that we have a little bit of time now ... so we're quite heartened by the low number of results that we've had."
Duthie said more surveillance and testing work was still needed. She said there was not much known about the parasite worldwide and it was looking into commissioning research to better understand the potential impacts on the fishery.
A rāhui was enacted in March, and Biosecurity New Zealand also put a controlled area notice in place in the 30 square kilometre zone of Foveaux Strait where the three infected oysters were found.
Duthie said it had met with the fishing sector, including quota holders, iwi and local authorities in Bluff today to discuss the response, including the rāhui.
"So that's something that we're going to [get] engagement with them [on] further, before we make a decision."