Authorities admit they may never know what triggered a white spot disease outbreak which shut down Queensland prawn farms and threatened to decimate the industry.
Seven prawn farms along the Logan River were shut down after the disease was discovered in December as officials worked to contain the outbreak.
"We may never know the cause of that outbreak," Lyn O'Connell from the agriculture department told a Senate estimates hearing on Tuesday.
Soon after the disease was discovered, retailers in the area were found selling and fishermen using contaminated raw prawns as bait.
These factors, along with an investigation into the "systemic circumvention" of biosecurity controls launched several months earlier, led to the January suspension of all uncooked prawns imports.
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The Queensland and federal governments are still working to determine the source of the white spot disease, which does not pose any risk to human health.
"Eradication is still the objective and is considered feasible," Ms O'Connell said.
Authorities have since stepped up prawn import inspections and worked alongside retailers and wholesalers to pull dodgy products from supermarket shelves and strip it from the supply chain.
The department meanwhile is pursuing action against importers suspected of deliberately evading biosecurity checks including revoking permits, rethinking approvals and sending a brief of evidence to commonwealth prosecutors.
The government has since allowed trade to resume for some "lower risk" items but will take some months to lift its halt on all prawn products.
"The suspension will remain in place until we can be certain the risks can be managed," Ms O'Connell said.
Despite tests proving there were contaminated prawns for sale around the Logan River, and the fact fisherman were found using those prawns as bait in the river, the government has not yet been able to ascertain how the infection occurred at the farms.
"In our mind, (they) continue to have to be dealt with as two separate issues until such time it can be proved one way or the other whether the cause of the outbreak was the infected imported prawns," Assistant Agriculture Minister Anne Ruston told senators.
