Wild fish near salmon farms contain antibiotics five times the allowed level

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

The Tasmanian Inquirer reports that the EPA released two monitoring reports in January showing 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.

Tassal used 32.5kg of oxytetracycline (OTC) in February 2023 and March 2023 at its Butlers lease near Bruny Island. The antibiotic was used to treat an outbreak of tenacibaculosis, which can affect the skin, mouth and gills, and kill affected fish. They used another 336kg of OTC at their Okehampton lease near Triabunna in May 2023 after detecting a Tasmanian Rickettsia-like organism, a bacterial infection that can result in significant production loss and some mortalities.

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 any use of antibiotics, salmon companies are required to test for residues in sediments near the treated cages and a few metres past the lease boundary, and also to do tests on wild fish caught in and beyond the lease area.

The report on the Butlers lease showed blue mackerel caught near the salmon pens had OTC residues almost five times the permitted level under the Australia New Zealand Food Standard Code. All the fish had feed pellets in their gut contents.

Australian salmon caught on the same day as the mackerel found OTC residues just under the allowed threshold. Flathead caught at a site about 2.5 kilometres from the salmon cages 64 days after the last use of medicated feed revealed OTC traces one-tenth the maximum residue limit.

This is not an isolated incident. 

In 2022, flathead caught off Coningham Beach, two kilometres from Tassal's Sheppards lease, contained OTC in their flesh above the reportable threshold.

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.

Read the detailed report in The Tasmanian Inquirer, 26 February 2025.