Salmon Farming – Antibiotic Resistance and Industry Crisis

Tasmanian salmon farming is facing a crisis due to heavy antibiotic use and resulting concerns over antibiotic resistance writes adjunct associate professor of chemical engineering at James Cook University in Townsville, Madoc Sheehan.

Tasmanian salmon farming – an industry in crisis

Science opinion.

Dead wildlife, threats of species extinction, fat globules washing up on beaches, heavy antibiotic use in intensive open-ocean salmon farming pens; it’s not what you imagine when you think of Tasmania’s clean green image.

With the EPA’s newly approved antibiotic (florfenicol), new fishing exclusion zones and growing concerns around antibiotic resistance – it’s getting difficult to argue that the Tasmanian Salmon industry is sustainable.

Is it even in the public’s interest?

Higher water temperatures, among other factors, has resulted in more disease and illness in Tasmanian farmed salmon. The industry response has been to throw antibiotic-laden feed at the problem.

In the summer of 2025, 15 thousand tons of salmon died¹, despite fish being fed with tons of the antibiotic drug – oxytetracycline. This particular antibiotic was largely ineffective at controlling disease and the industry, with the support of the EPA, has moved on to a new antibiotic – florfenicol.

As humans we rely on a range of different antibiotics. They are vital tools of our health system, used to manage infections.

When you take antibiotics, bacteria die and you can recover from infection. Before antibiotics and the discovery of penicillin, humans would die or have limbs amputated from simple infected cuts. Antibiotics have saved and continue to save millions of us. Were our antibiotics to lose their effectiveness and bacteria and microbes to become “resistant” to their effects, many more millions of us would die. The World Health Organisation states that without action to reduce antibiotic resistance² and protect the efficacy of our antibiotics, by 2050 we can expect to see more than 10 million humans die each year³.

Florfenicol (and oxytetracycline) are antibiotics commonly used in aquaculture, including in farmed salmon produced in Tasmania, Chile and Norway.

Antibiotics, including florfenicol and oxytetracycline, are themselves toxic at very low concentrations, creating a health hazard for workers who handle feeds. When fed to salmon in feed, up to 70% of the antibiotics can remain unused, transferring to the local environment. Un-metabolised antibiotics simply fall through the pen as uneaten feed or as fish feces, settling onto the sediment below the pens or moving into the water column and spreading. When they absorb to sediments they can accumulate and build up over time⁴. In some world markets, just the presence of antibiotic residues, even at trace levels, can make fish unsaleable.

There has been a focus in the media and by the EPA on the safety of the antibiotics themselves, arguing that as long as you are far enough away from the pens, you’ll be ok; thus the introduction of 3km exclusion zones⁵.

Despite its obvious and severe impacts on recreational fishing, it’s an old-school “solution to pollution is dilution” model.

Regulating the public, rather than the industry that creates the harm, ignores sustainability and best practice. It also conveniently ignores the elephant in the room – antibiotic resistance – and the grave harm that poses to all of us.

When bacteria and microorganisms in the environment and in fish are exposed to antibiotics there is a selective pressure. Those bacteria that harbor a natural resistance to antibiotics are more likely to succeed, in comparison to bacteria with no resistance.

Under such pressure, microbial diversity decreases and antibiotic resistant microbes increase their abundance. Microbes may also contain antibiotic resistant genes that can move to other bacteria, through a process called horizontal gene transfer, spreading the antibiotic resistance to new bacteria and microbes. These genes can remain in the environment for years after antibiotic treatments. In the worst case scenario, microbes can acquire multi-drug resistance, becoming literal “super bugs”. Other human antibiotics – those that are not even used salmon farming – can be rendered ineffective in the face of such super-bugs.

In Chilean salmon farming, both florfenicol and oxytetracycline have been extensively used to control the same bacterial disease seen in Tasmanian salmon farming. Fish death has been rampant in these pens as well. There is also evidence of super resistant bacteria coming from these florfenicol-treated fish farms.

Genetic studies⁶ of fish feces and fish intestines in these waters have shown a high degree of antibiotic resistance in fish gut bacteria. Most worryingly, when florfenicol resistant bacteria were tested against eight other human antibiotics (e.g. ciprofloxacin, ampicillin and erythromycin), 4% of the florfenicol antibiotic resistant bacteria were also resistant to all eight tested antibiotics. Most of these resistant bacteria (96% of them) contained genetic elements considered highly transferable.

In another study⁷ of Chilean fish farms using the antibiotic florfenicol, mussels both near and far away (e.g. 30km) from fish farms where investigated. Mussels are a good indicator of environmental impact because they filter and concentrate environmental microorganisms. As antibiotic use increased in these farms, microbial diversity decreased, with mussels closest to the fish farms most impacted. The lack of diversity in microorganisms, being worse closest to the farms, can exacerbate the problems faced by disease-prone fish farms. It’s a slippery slope… more antibiotic use can lead to more of the same organisms that lead to the disease in the first place, but with new found antibiotic resistance.

It suggests a downward spiral of more fish deaths and more antibiotics, with the losers being the environment, public and industry workers.

More effective industry and food safety regulations are a sure-fire way to reduce the impacts of industrial fish farming on both the environment and us. For example, in Norway, antibiotic use is highly regulated and preventative measures such as vaccination, monitoring and rezoning of production facilities have helped significantly reduce antibiotics use⁴.

Over 25 years, much tougher regulations helped Norwegian producers reduce antibiotic use from 48 tonnes to ½ tonne per year, whilst simultaneously doubling production. Clearly there are more sustainable ways to farm salmon than what is currently happening.

Tasmanian regulators should take note and look to Europe for best practice regulation in fish farming.

There is great urgency in improving and reducing antibiotic use in Tasmanian salmon farming. Acting now is essential, before the next multi-drug resistant pathogen emerges from a salmon farm, potentially creating an untreatable epidemic.

1. 1. https://www.abc.net.au/news/2025-11-03/tasmanian-government-salmon-mortality-report/105964772
   2. https://www.who.int/news/item/13-10-2025-who-warns-of-widespread-resistance-to-common-antibiotics-worldwide
   3. https://wellcomecollection.org/works/rdpck35v/items?shouldScrollToCanvas=true
   4. https://onlinelibrary.wiley.com/doi/10.1111/raq.12344
   5. https://www.health.tas.gov.au/news-sajari/news/advice-public-health-about-recreational-fishing-dentrecasteaux-channel-and-adjacent-waters
   6. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0203641
   7. https://doi.org/10.1016/j.envres.2021.112068

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