Tasmania’s largest salmon company, Tassal, has revealed wild fish at one of its salmon 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.
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 late February 2023 and early March 2023 at its Butlers lease near Bruny Island national park. The antibiotic was used to treat an outbreak of tenacibaculosis, a disease that can damage the skin, mouth and gills and kill affected fish.
The company used 336kg of the same antibiotic to treat salmon at its Okehampton lease near Triabunna in May 2023. The EPA reported that it followed Tassal detecting a Tasmanian Rickettsia-like organism, 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”. It described this as “one of the biggest threats to global health”, and has recommended the vaccination of farmed animals as a strategy to reduce the overuse of antibiotics.
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 200µg/kg.
The report on the Butlers lease revealed a sample of three blue mackerel caught near the salmon pens had OTC residues of 960µg/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.
The report by Aquenal, an environmental consultancy, noted that Tassal requested that the sample be retested to check for “possible erroneous data”. Aquenal reported the second test was consistent with the initial result.
A sample of three Australian salmon caught on the same day as the mackerel found OTC residues of 180µg/kg, just under the 200µg/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 20µg/kg, one-tenth the maximum residue limit.
Tasmanian Inquirer sought comment from Tassal, but the company did not respond.
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 100μg/kg. Our regulators should be striving for the world’s best practice, not pandering to industry,” he said.
The EPA said that, despite the initial high result in blue mackerel, there was no need to undertake additional testing before the second round of testing after 64 days had elapsed.
Narkowicz said blue mackerel with 960µg/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”.
“Wild fish that thousands of Tasmanians catch and eat should contain no antibiotics at all. Australian salmon travel long distances. There is no guarantee that they will be antibiotic-free even if they are caught nowhere near a salmon farm,” he said.
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 20µg/kg.
The EPA told Tasmanian Inquirer that given OTC was not detected in samples from that salmon farm it was possible another source of OTC may have “impacted this fish sample”.
Neill said Food Standards Australia should review the use of OTC in fish for human consumption, and the amount of allowable OTC in salmon should be changed to match European standards.
