We believe that disease control in salmon requires a holistic approach. Good site management, fish husbandry and rigorous biosecurity measures are central to reducing the risk of disease outbreaks and controlling the spread of infectious diseases.
Vaccines are important in preventing disease outbreaks but cannot control all losses. Medication such as antibiotics are also important but should only be used as a last line of defence to avoid significant animal welfare issues and stock losses. This mind-set means that we are continually working to develop proactive diet regimes and vaccines to allow our salmon to combat known illnesses and lead healthy lives.
If our vets feel there is a need to treat fish with antibiotics, it is supervised, reported and strictly regulated by government. The antibiotics are allowed to pass through the fish long before it is harvested, in accordance with regulatory requirements. Independent residue testing demonstrates that our harvest fish contain no antibiotics, and this information is published annually on the National Residues Survey website.
Our investments in Recirculation Aquaculture System (RAS) facilities have been a big step forward in ensuring the water used to grow our young fish is filtered and disinfected. This minimises exposure to potential disease agents via the incoming water, meaning fish are even less likely to be exposed to bacteria that have resulted in antibiotic treatments in the past. This, combined with the continuing development of vaccines and improvements to farming practices, has set us on a path where the use of even occasional antibiotic treatments in salmonid farming is becoming very uncommon.
Lonnavale was our first RAS facility, representing a shift from our traditional flow-through style hatcheries. Forest Home (at the time) represented the second generation of our recirculation hatcheries while Whale Point is the future; it includes a state of the art internal water treatment system which enables the facility to reuse 98 per cent of its water; the remaining 2 per cent can be reused offshore for bathing.
- Huon has not used antibiotics at sea since 2016 when a single pen was treated. Furthermore, we have not used antibiotics at any of our Huon owned land-based sites (i.e. hatcheries) since January 2019.
- The correct use of antibiotic is critical in reducing antimicrobial resistance which is why our Vets/fish health teams follow the World Health Organisation (WHO) guidelines for the use of antibiotics in livestock industries.
- WHO does not preclude the use of antibiotics in livestock industries, including salmon farming.
- Our Vets only prescribe antibiotics as a last resort and always following a full investigation, confirmation of diagnosis through laboratory testing of fish health samples and after confirming antibiotic sensitivity of causative organisms.
- Huon voluntarily publicly reports all antibiotic use (marine and freshwater) as well as reporting their use to the State Government in real time. The wording of this should be changed as we only report marine use to government.
- Antibiotics are prescribed by a qualified veterinarian and there is a strict withholding period which means that any traces are completely passed through the fish long before it is harvested.
- Huon also participates in an annual national residue survey to monitor levels of therapeutants, ensuring we comply with National standards.
A last resort
We believe that antibiotics should only be used as a last resort which is why we practice a holistic approach to farming. Integral to our approach is good site management, low stocking densities, the development and use of vaccines, feeding a high-quality diet, and keeping our fish as calm and low stress as possible.
It has been five years since we have used antibiotics at sea, which was to treat a single pen of fish.
In January 2019, we needed to use antibiotics to treat some of our small fish grown at one of our flow-through freshwater hatcheries. These fish were prescribed the treatment as they had Yersinia (a coccobacilli bacterium which is naturally present in the river the flows into the hatchery). The treatment was highly successful and effectively resolved the infection. To avoid needing to treat fish in this way in future, we have since changed our stocking practices so that these small salmon are instead grown in our newer, recirculation hatchery systems, where they should not come into contact with the Yersinia bacterium at all.
Huon does not use any of the antibiotics listed as Critically Important by the WHO – despite WHO guidelines stating that this would be acceptable under certain defined circumstances. This ensures that we preserve those Critically Important antibiotics for human use only. Of the other antibiotics available for use, Huon would only ever use an antibiotic that is confirmed to be effective against the causative disease organism – which is done through testing at our local Fish Health laboratories. This way, we can be sure that we are following best practice in terms of antibiotic stewardship.
(WHO categorises all antimicrobials used in human medicine as either Critically Important, Highly Important or Important in the medically treatment of bacterial infections in humans; in effect placing a value/importance on each antimicrobial in terms of its effectiveness in combating bacterial infections).
The Tasmanian industry as a whole independently made the decision many years ago not to use antibiotics such as Oxolinic Acid (Quinolone) and Amoxycillin (Penicillin) which are compounds listed by the WHO within Critically Important classes of antimicrobials. This decision was made despite these particular antibiotics being used in salmon farming across other countries.
Preventing antibiotic resistance
To prevent and control the spread of antibiotic resistance, the agriculture sector (including aquaculture) can:
- Only give antibiotics to animals under veterinary supervision.
- Not use antibiotics for growth promotion or to prevent diseases in healthy animals.
- Vaccinate animals to reduce the need for antibiotics and use alternatives to antibiotics when available.
- Promote and apply good practices at all steps of production and processing of foods from animal and plant sources.
- Improve biosecurity on farms and prevent infections through improved hygiene and animal welfare.
Voluntary public reporting
We recently undertook to publicly and voluntarily report our antibiotic use. The table below demonstrates how the use of antibiotics at Huon Aquaculture has continued to reduce, with no treatments at any of Huon’s Marine or Freshwater sites last year:
|Over Calendar Yr||Hatcheries||Marine Pens treated|
Withholding period and residue testing
In the event that antibiotics are used in a population of fish at sea, we adhere to strict withholding periods which allows any therapeutants to pass through the fish long before it is harvested for consumption.
In addition, every year Huon participates in an independent, national residue survey to monitor levels of a wide variety of compounds and therapeutants, ensuring we comply with National standards. These surveys consistently demonstrate that our harvest fish contain no antibiotics, and the results can be found on the National Residues Survey website: https://www.agriculture.gov.au/ag-farm-food/food/nrs.
On occasion we also conduct additional, voluntarily flesh testing which is not required by government regulations. When we do this, we also publish the results on our website.