Revealed: 16 ‘toxic’ chemicals fish farmers are allowed to use

Fish farmers in Scotland are permitted to use 16 “toxic” chemicals to kill parasites and fungi, control infections and anaesthetise fish, according to the Scottish Government’s green watchdog.

The Scottish Environment Protection Agency (Sepa) has disclosed all the pesticides, fungicides, antibiotics and anaesthetics it allows companies to discharge from salmon cages into dozens of lochs around the country.

Environmental groups have expressed concerns about the “toxic effects” of the chemicals on wildlife. They have called for improved monitoring and a halt to fish farm expansion until “meaningful action” is taken to curb the risks.

The industry, however, stressed that the chemicals were used responsibly in line with official authorisations. It pointed out that its spending on fish farm medicines had more than halved since 2015.

In response to a request from The Ferret, Sepa listed five anti-parasite chemicals, six antibiotics, two fungicides and three anaesthetics that were currently “authorised for discharge”. The authorisations include freshwater as well as saltwater lochs.

The parasiticides include emamectin, marketed as Slice, azamethiphos and hydrogen peroxide. These are used to kill the sea lice that can infest caged salmon — but they can also harm wildlife, as The Ferret has previously reported.

One of the permitted fungicides is formaldehyde, which can cause cancer in humans and is used to embalm corpses. The antibiotics are used to treat a series of diseases that salmon can suffer, while the anaesthetics are to numb fish when they are being handled.

The chemicals fish farmers are allowed to use

Emamectin benzoateagainst parasites
Azamethiphosagainst parasites
Deltamethrinagainst parasites
Hydrogen peroxideagainst parasites
Cypermethrinagainst parasites (no longer available in UK)
Bronopolagainst fungi
Formaldehydeagainst fungi
Amoxycillin trihydrateagainst disease
Oxolinic acidagainst disease
Oxytetracycline hydrochlorideagainst disease
Sulphadiazineagainst disease
Trimethoprimagainst disease
Florfenicolagainst disease
Ethyl-amino benzoateanaesthetic
Tricaine methyl sulphonateanaesthetic
Source: Scottish Environment Protection Agency

The National Trust for Scotland, a conservation charity with more than 365,000 members, is worried about the damage that the chemicals could do. “We are concerned at the toxic effects on sea life that can arise from chemical treatments on farmed salmon,” said the trust’s head of conservation, Stuart Brooks.

“We have been highlighting the need for usage of these chemicals to reflect the evidence of harm that is emerging. The trust supports the conclusions of the Scottish Parliament’s rural economy committee that meaningful action needs to be taken to address these environmental issues before the industry can expand.”

The Scottish Wildlife Trust, which describes itself as Scotland’s leading nature conservation charity, agreed that further growth of the industry cannot come at the expense of healthy seas. “A number of chemical treatments are applied in Scottish aquaculture and it’s important to take a precautionary approach to their use,” said the trust’s living seas manager, Dr Sam Collin.

“To minimise any negative impact on wildlife these treatments must be subjected to rigorous and independent assessment before they enter the marine environment. Continued careful monitoring of the effect of chemicals on the wider environment is also needed.”

Collin added: “If any unforeseen impacts are detected then these must be quickly mitigated, or the chemicals concerned should be withdrawn from use. We believe both the industry and regulators including Sepa must improve their monitoring.”

The wild fish campaign group, Salmon and Trout Conservation Scotland, argued that the salmon industry was “intensive factory farming” that polluted lochs. Sepa should be “far more precautionary”, said the group’s solicitor, Guy Linley-Adams.

“The main problem is that Sepa always seems to give the benefit of the doubt — of any scientific uncertainty — to the fish farmers, and so the environment suffers.”

Fish farmers in Italy, who rear trout, sea bream and sea bass instead of salmon, have highlighted that Scottish fish farms can use more chemicals than they can. Seven chemicals have been authorised at Italian fish farms, including five antibiotics, one anaesthetic and a disinfectant no longer available in Italy.

Pier Antonio Salvador, head of the Italian fish farmers’ association, thought that it was “not right” that more chemicals could be used in Scotland. “There are many things that should be fixed,” he said.

But according to the Scottish Salmon Producers Organisation (SSPO), it is “highly misleading” to compare the fish farming systems in Scotland and Italy. “Knowing the number of different medicines allowed for use in any aquaculture system provides just that — a knowledge of the number,” said a spokesperson for the industry group.

“It does not reveal the quantities of medicines used and it is these statistics which are crucial to understanding what is really going on. We know, for example, that the amount spent on medicines by the Scottish salmon farming sector fell by 47 per cent between 2015 and 2018, a trend that has continued ever since.”

The spokesperson pointed out that all the chemicals it was allowed to use were appraised and approved by Sepa and the Veterinary Medicines Directorate “by balancing the welfare of animals with the unique wild environment in which they are reared”.

Having a range of products was “positive” as it provided options for the responsible use of medicines to manage the health and welfare of fish, SSPO suggested. This was the same approach that doctors took in the provision of medicine for human health, it argued.

The Scottish Environment Protection Agency stressed that it had “one of the strongest regulatory regimes” for fish farming in the world. “The number of medicines that fish farmers can use in Scotland is in line with other salmon producing nations in Europe,” said the agency’s head of ecology, Peter Pollard.

“Unlike some major salmon producing countries, our approach also has the added control of requiring those medicines discharged in significant quantities to meet environmental standards. Sepa only licences discharges to the limit of what the local environment can accommodate sustainably.”

Pollard added: ”Whilst the long term trend has been for reduced reliance on medicine treatments, we continue to work with the finfish aquaculture sector on innovation and containment, alternatives to medicine use and site relocation. Progress has been made in each of these areas.”

On 16 March 2021 The Ferret published internal emails revealing that Scottish Government research into pesticides used to control lice deliberately excluded impacts on the “wider marine environment”. We reported on 14 March that six fish farming companies in Scotland given government hand-outs of over £10 million had made profits of £926 million since 2010.

This story is the third in a series on fish farming funded by journalismfund.eu, an independent, non-profit organisation in Brussels that supports cross-border investigative journalism. Our investigations were carried in partnership with the Italian journalist, Francesco De Augustinis.


This story was changed at 14.55 on 17 March 2021 to add quote marks around the word toxic, following representations from the Scottish Salmon Producers Organisation. Additional links were also added. Cover image with thanks to Corin Smith.

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