Salmon company to inject fish with antibiotics ahead of expected marine heat wave

A salmon company will begin individually injecting diseased fish in Tasmanian waters with an antibiotic this week, in what it says is a new practice for the state.

Tassal, the Canadian-owned seafood giant, said it will use oxytetracycline (OTC) to treat a bacterial outbreak in fish at a lease in Tasmania's south, in the D'Entrecasteaux Channel, on Thursday.

The announcement follows the salmon industry's controversial use of the antibiotic florfenicol last summer, which was dispersed in the water with salmon food.

Both antibiotics treat disease in farmed salmon caused by the bacteria Piscirickettsia salmonis, which has led to mass fish deaths when waters warm during the summer months in recent years.

The resultant dead fish and the proliferation of antibiotics in the marine environment have made the industry the subject of the ire of environmentalists, swimmers, recreational fishers and the wild fisheries sector.

Tassal waiting for approval to use banned antibiotic again

Ahead of last summer, the Australian Pesticides and Veterinary Medicines Authority (APVMA) approved the industry's use of florfenicol in southern Tasmanian waters.

The APVMA retracted the licence in March, citing an "unacceptable risk of residue exposure to non-target species".

In the first three months of this year, the industry used more than five tonnes of florfenicol trying to control a disease outbreak that killed 9,000 tonnes of farmed fish.

In a statement today, a Tassal spokesperson said the company was waiting for approval to once again use florfenicol to treat disease outbreaks.

"Florfenicol in feed is the most effective option, and while we await a permit for it, we're using OTC where required," they said.

OTC has been used by the industry in the past, but the spokesperson said this would be the first time it is used to treat fish at sea.

They said about 10 kilograms of OTC would be used in the first pen on Thursday, with fish individually anaesthetised, injected and then monitored for recovery.

Despite the preference for florfenicol, Tassal said direct injection of OTC uses "a fraction of the medicine needed for medicated feed and is expected to deliver a more targeted treatment".

Tassal rival Huon Aquaculture tried to use OTC to overcome disease outbreaks in coastal pens last year, but ruled it "largely ineffective" before the first florfenicol approval.

At the time, the industry argued florfenicol had a range of advantages over oxytetracycline because it required lower dosages, lower levels were excreted by fish, and it had lower toxicity for aquatic organisms.

Animal welfare a top priority, industry says

John Whittington, the chief executive of industry body Salmon Tasmania, said he was bracing for a marine heatwave this summer.

He said across the industry, fish were being bred and fed for resilience to warmer waters, and would be vaccinated against disease before being released into pens.

But, he said, florfenicol remains the best treatment option for disease outbreaks, and the industry planned to use it as soon as possible, if approval is granted by the APVMA.

"We are doing everything we can to ensure the welfare of our animals over summer is maintained," Dr Whittington said.

However, he said the industry was also aware of how its use of florfenicol might affect wild fisheries such as rock lobster and abalone.

A Tasmanian government spokesperson said any decision regarding florfenicol was the responsibility of the APVMA, but they expect the salmon industry to "work constructively with the wild catch sector in their shared environment".

They also said they expected the salmon industry to work with commercial fishers on the question of any compensation that may be required if antibiotic use leads to the closure of fisheries, as occurred last summer.

Greens MP Vica Bayley said the use of antibiotics was not sustainable.

The APVMA was contacted for comment.