Published: 20 January 2025 Updated: 29 January 2025
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DATE 29 Jan 2025
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FEEDBACK/STORY SUGGESTIONS Dempsey Ward Communication Coordinator +61 2 6122 2134 dempsey.ward@frdc.com.au

The safe and effective use of the chemical trichlorfon has been validated for use on Australian prawn farms to prevent the spread of the devastating white spot disease.

By Catherine Norwood 

Prawn farms enhance biosecurity through filtration and chemical treatment of water supplies, particularly in areas affected by white spot disease, a highly contagious and deadly infection of prawns, and many other crustaceans.  

Wild glass shrimp infected with white spot disease represent a biosecurity risk for prawn farmers
Wild glass shrimp infected with white spot disease represent a biosecurity risk for prawn farmers. Photo: QDPI 

 

To support the need for increased biosecurity, the Australian Prawn Farmers Association (APFA), through its Industry Partnership with FRDC, supported a project (2021-026) that has validated the widely used agricultural chemical trichlorfon as part of a safe disease prevention strategy for prawn farmers.

APFA funded the research as an industry priority, to provide greater confidence for regulators and farmers in the safety of trichlorfon use and its effects within prawn farms.  

New treatment option

Lead researcher David Mann, from QDPI, says white spot disease was first detected on prawn farms in Queensland in 2016. Chlorine was used at the time to decontaminate the seven affected farms.  

Researcher David Mann preparing a dose of trichlorfon for tank trials at the QDPI Bribie Island Research Station
Researcher David Mann preparing a dose of trichlorfon for tank trials at the QDPI Bribie Island Research Station. Photo: QDPI 

 

Since then, trichlorfon has emerged as a better alternative for the treatment of water supplies prior to production, and for decontamination of affected farms, says David. 

As a preventive, water is treated with trichlorfon before it enters prawn ponds, or filled in ponds before prawns are stocked. In 2023, it was also used to decontaminate prawn farms in the Yamba region of NSW that were affected by a white spot disease outbreak. 

Essentially, trichlorfon kills crustaceans of all types, from the microscopic copepods that form part of ocean plankton to larger animals including prawns. 

The Australian Veterinary Medicines and Pesticides Authority (APVMA) issued a Minor Use Permit for trichlorfon as a ‘crusticide’ for prawn farms in 2017 and prawn farmers have since used it as a preventative treatment in new biosecurity measures. 

“It is widely used in the Southeast Asian prawn farming sector, where some countries have been affected by white spot disease for about 30 years,” says David. 

“Our research has filled an information gap, scientifically validating the effectiveness of the chemical and its breakdown to undetectable levels under tropical and subtropical conditions typical of Australian prawn farms.” 

Commercial application

FRDC funded the research as an industry priority, to provide greater confidence for regulators and farmers in the safety of trichlorfon use and its effects within prawn farms. 

“Trichlorfon is highly targeted, affecting only crustaceans in the water,” explains David. 

“By killing crustaceans, it eliminates potential carriers of the white spot syndrome virus, which causes the disease, rather than killing the virus itself. It is 99 per cent effective in killing potential crustacean hosts.”

David and his team at QDPI used tank trials at the Bribie Island Research Centre and field trials on two commercial properties to test the degradation rate of the chemical.

Trichlorfon field trials were conducted at two commercial prawn farms.
Trichlorfon field trials were conducted at two commercial prawn farms. Photo QDPI 

 

Trichlorfon has a half-life of around one day under commonly encountered conditions.  

“The relatively rapid degradation of trichlorfon to non-harmful products is an advantage,” says David. “By day 17 after treatment – which is the required withholding period – it will have degraded to undetectable levels.”  

Chair of the Australian Prawn Farmers Association, Tony Charles, says the project has strengthened the industry’s farm biosecurity options. 

“White spot syndrome virus continues to be found in the wild and remains a persistent threat for prawn farmers using ocean water in their operations. 

“This research means farmers can be confident that potential vectors for pathogen introduction via incoming water are significantly reduced. The farmer-friendly user guide produced by the project is also a valuable resource for the industry,” adds Tony.  

Related FRDC Project  

2021-026: Water disinfection for influent water biosecurity on prawn grow-out farms 

FRDC White Spot Disease Page: https://www.frdc.com.au/white-spot-disease