High antibiotic levels in wild fish, low-level antibiotic traces up to 7 km from Tassal farms

Pellet feed loading - Bob Burton photo
Pellet feed loading - Bob Burton photo

Tasmania's largest salmon company, Tassal, has revealed wild fish at one of its farms contained antibiotic residues at almost five times the allowed level. In another case, there were low-level antibiotic traces in wild fish caught more than seven kilometres from another Tassal salmon farm.

Tasmanian Inquirer report, 26 February 2024

Two monitoring reports published by the Environment Protection Authority (EPA) in January show Tassal used 368.5 kilograms of a controversial antibiotic to control disease outbreaks at the two salmon farms last year. There was no public notification when the antibiotics were used or when the monitoring reports were released.

Sheenagh Neill, a spokesperson for Marine Protection Tasmania, said she was concerned about the continuing secrecy surrounding antibiotics use in public waterways. "The community is still not being informed promptly despite the 2022 Legislative Council inquiry into the fish farming industry recommending the 'timely' release of information on the use of antibiotics," she said.

Tassal used 32.5kg of oxytetracycline (OTC) in February and March 2023 at its Butlers lease near Bruny Island National Park to treat tenacibaculosis, a disease that can damage the skin, mouth and gills and kill affected fish. They used 336kg to treat salmon at the Okehampton lease near Triabunna in May 2023 for a bacterial infection that can result in significant production loss and cause the death of some affected fish.

The World Health Organization classed OTC as "highly important" for human health, and warned its overuse in the food industry could lead to the development of antibiotic-resistant "superbugs".

After the use of antibiotics, the EPA requires salmon companies to test for residues in sediments near the treated cages and a short distance from the lease boundary. It also requires tests on wild fish caught in and beyond the lease area. All samples with OTC equal to or greater than 100 micrograms per kilogram (µg/kg) must be reported. The maximum residue standard in food for human consumption is 200 µg/kg.

The report on the Butlers lease revealed a sample of three blue mackerel caught near the salmon pens had OTC residues of 960 µg/kg, almost five times the permitted level under the Australia New Zealand Food Standard Code. All the fish had feed pellets in their gut contents.

A sample of three Australian salmon caught on the same day as the mackerel found OTC residues of 180 µg/kg, just under the 200 µg/kg threshold. A sample of three flathead caught at a site about 2.5 kilometres from the salmon cages 64 days after the last use of medicated feed revealed OTC residue of 20 µg/kg, one-tenth the maximum residue limit.

It is not the first time wild fish with OTC residue have been detected well beyond a salmon farm. In late 2022, it was revealed that flathead caught off Coningham Beach, two kilometres from Tassal's Sheppards lease, contained OTC in their flesh above the reportable threshold.

Dr Christian Narkowicz, an organic chemist, said Australia's maximum residue standard for OTC was high compared to other countries. "Europe has a maximum residue limit of 100 μg/kg. Our regulators should be striving for the world's best practice, not pandering to industry," he said. Blue mackerel with 960 µg/kg of OTC residue in their flesh were "not fit for human consumption" and described the 64-day delay in further testing as "not good enough".

The monitoring report for the Okehampton lease revealed that three flathead caught at a site near Maria Island, more than seven kilometres away from the treated pens, contained OTC at 20 µg/kg.