Half a Billion Cleaner Fish Paid the Price for Farmed Salmon

Norway’s salmon farming industry used more than half a billion cleaner fishes before establishing whether the practice worked.

Between 1998 and 2024, salmon farms deployed 510,833,000 lumpfishes, ballan wrasses and wild-caught wrasses inside sea cages. Their purpose was to eat parasitic lice from the bodies of farmed salmon. They were used as living pest-control devices.

The experiment failed.

Cleaner Fish Became Disposable Equipment

Salmon lice are a predictable consequence of imprisoning huge numbers of salmon together in open-net cages. The parasites attach themselves to the fish, damaging their skin and causing open wounds, infections and death. Rather than question the farming system responsible, the industry searched for another animal to control the problem.

Cleaner fishes appeared to provide a convenient biological solution. Instead of relying entirely on chemicals, farmers could place wrasses and lumpfishes inside cages and allow them to remove lice from the salmon. The idea was promoted as effective and environmentally responsible. It was rapidly expanded despite limited evidence from commercial farms.

Cleaner fish use in Norway peaked in 2019, when more than 61 million individuals were stocked in a single year. By 2024, the figure had fallen to 22.5 million.

Researchers have now identified four main reasons for the decline: uncertain effectiveness, horrific mortality, newer lice-control technologies and stricter regulation.

Most Cleaner Fishes Were Not Cleaning

Early trials suggested that cleaner fishes could reduce lice numbers. However, these experiments used smaller cages, fewer salmon and much shorter study periods than commercial farms. The results did not translate well to industrial conditions. An analysis of 488 Norwegian farms found that cleaner fishes only slightly delayed the need for the first lice treatment. Results varied considerably between farms.

The largest study of lumpfishes examined nearly 25,000 individuals across 80 farms. Only around 3% had lice in their stomachs. Most cleaner fishes were not eating lice most of the time. The industry had scaled up the use of millions of animals based on evidence that did not reflect the conditions in which they would actually be confined.

Some Farms Lost Every Cleaner Fish

Cleaner fishes were placed in an environment designed around salmon production, not around their own needs. They were transported into cages with conditions fundamentally different from their natural habitats. They faced bacterial, parasitic, fungal and viral diseases. Many became emaciated. Others were injured during mechanical lice treatments intended to protect the salmon.

Artificial shelters, additional food and health inspections were introduced in attempts to keep more of them alive. These measures required labour and money, while failing to demonstrate that mortality had been brought under control.

A national survey by the Norwegian Food Safety Authority found that half of farmers reported no cleaner fishes remaining when the salmon were sent to slaughter. That suggests mortality of 100% in those cages.

The cleaner fishes had simply disappeared from the production system through death.

The industry describes them as “cleaner fish” because their value is defined by the service humans expect them to perform. Once they fail to remove enough lice, become ill or die, they become another production loss.

Salmon Farming Multiplies The Number Of Fishes Killed

Cleaner fishes are only one group sacrificed to produce farmed salmon. Salmon are carnivorous. Farming them requires fishmeal and fish oil produced from wild-caught fishes such as anchovies, sardines and mackerels.

Research suggests the number of wild fishes used in aquaculture feed has been substantially underestimated. Traditional calculations often exclude capture deaths, unwanted fishes caught alongside target species and wild fishes hidden within ingredients classified as “trimmings”. Updated estimates found that aquaculture’s wild-fish inputs may be up to 307% higher than previously reported.

Salmon farming alone can require between 1.86 and 6.24 pounds of wild fishes for every pound of salmon produced.

The system does not save wild fishes. It catches them in vast numbers, reduces them to feed and uses them to fatten other fishes for wealthier markets.

European demand for wild fishes used in aquaculture feed is projected to increase by 70% by 2040. This could mean between 83 billion and 192 billion individual fishes being caught for feed every year. Wild fishes are killed to feed farmed salmon. Cleaner fishes are confined and killed to protect those salmon from parasites. The salmon themselves are eventually killed for human consumption. This is not efficient food production. It is a hierarchy of exploitation.

Mass Death Is Built Into Salmon Farming

The cleaner fish disaster cannot be separated from the wider salmon farming industry.

Inspection reports released in Britain revealed repeated incidents in which enormous numbers of farmed fishes died through poisoning, oxygen loss and negligence. More than 100,000 salmon suffocated at one facility after a worker left them unattended and their oxygen supply stopped.

At the same site, hydrogen sulphide killed more than one million fishes in ten hours.

At another farm, 600,000 fishes died following hydrogen sulphide exposure. When the problem happened again, more than 1.5 million died.

Authorities reportedly took no enforcement action over several of these incidents.

The industry continues to promote strict standards, advanced technology and responsible production. Yet mass death is not an unusual interruption to the system. It is repeatedly recorded across farms built around crowding, disease and mechanical control.

When activists filmed salmons with severe lice infestations, damaged bodies and twisted spines, the response went beyond public relations.

A salmon farming company commissioned an intelligence report containing information about campaigners’ addresses, phone numbers, businesses and social media activity. The report proposed covert surveillance and the use of a false identity to search for financial difficulties.

Private operatives later followed and photographed two campaigners. It is difficult to reconcile claims of transparency with an industry monitoring the people documenting what happens inside its cages.

New Technology Does Not Make Salmon Farming Ethical

Cleaner fish use has partly declined because farmers now have other ways to control lice.

These include physical barriers, systems that manipulate swimming depth, specialised feeds and lasers designed to target parasites.

These methods may reduce the number of cleaner fishes used. They do not address the captivity and slaughter of salmon or the wild fishes caught to feed them.

The researchers recommend phasing out lumpfishes and wild-caught wrasses by 2029. Farmed ballan wrasses should also stop being used unless the industry can prove commercial effectiveness and reduce mortality to 5%.

Ending the use of cleaner fishes would prevent millions of animals from being treated as disposable equipment. But replacing one lice-control method with another does not transform salmon farming into an ethical industry.

The cages remain. The parasites remain. The feed fisheries remain. The slaughter remains.

Salmon Is Not Necessary

Nobody needs to eat salmon. Plant-based alternatives are already available in major British supermarkets. Vivera produces salmon-style fillets, while Squeaky Bean sells smoked salmon-style slices and ready-to-eat salmon-style flakes. Biff’s also offers smoked salmon-style slices made from rice, konjac and beetroot. These products provide familiar flavours and textures without imprisoning salmon, sacrificing cleaner fishes or catching wild fishes to produce feed. More than half a billion cleaner fishes were used because the salmon industry created a parasite problem and wanted another animal to solve it.

They were not failed technology.

They were individuals who were treated as technology.