The Rise And Fall Of Cleaner Fish Use In Norwegian Salmon Farming

“Cleaner fish” is a term used to describe a collection of species, including ballan wrasses and lumpfishes, that clean parasitic lice from other fishes. Cleaner fishes are often used by fish farmers to boost the health and survival of species such as salmons that are farmed for consumption. In Norway, for instance, 510,833,000 wild and farmed cleaner fishes were used on farms between 1998 and 2024.

Norway’s rapid expansion of cleaner fish use wasn’t purely due to demand. In the early 2000s, the country invested heavily in Atlantic cod aquaculture only to see that industry collapse between 2008 and 2012 from disease, economic pressures, and an increase in wild cod fishery quotas. When cod farming failed, the hatcheries needed a new purpose, and cleaner fish production filled the gap. Combined with the spread of louse resistance to chemical treatments, this created conditions for widespread adoption.

Cleaner fish use in Norway peaked around 2019 at over 61 million individuals stocked, but has since significantly declined to just 22.5 million in 2024. This article identifies four main reasons for this downward trend: limited evidence on effectiveness, poor welfare outcomes, better alternatives, and changes in regulation and enforcement.

Limited Evidence On Effectiveness

Commercial adoption of cleaner fishes for removing lice from salmons followed only a few experimental trials suggesting it would be effective. These studies were conducted with smaller cages and far fewer salmons and over much shorter timeframes than real-world farm conditions. Results from large-scale research have been more mixed. An analysis of 488 Norwegian farms, for example, found that cleaner fishes only slightly delayed the time to first louse treatment on average, with effects varying widely from farm to farm. Moreover, in the largest study of lumpfishes to date — covering nearly 25,000 individuals across 80 farms — only about 3% actually had lice in their stomachs. Most cleaner fishes, most of the time, are simply not cleaning, and farmers likely found that using them didn’t work as well as they expected.

Poor Welfare Outcomes

In fish farming, cleaner fish welfare takes a backseat to salmon welfare. To begin with, cleaner fishes are transported to the salmons’ natural environment, which is fundamentally different from their own requirements. They’re also vulnerable to many bacterial, parasitic, viral, and fungal diseases. Physical injuries from mechanical delousing treatments are common, and emaciation is widespread. Taken together, these conditions can sometimes lead to catastrophic consequences: according to a national survey from the Norwegian Food Safety Authority, half of farmers reported that no cleaner fishes were left in cages when the salmons were delivered for slaughter, indicating 100% mortality. While farmers have attempted to improve cleaner fish welfare through measures such as providing artificial hides, supplemental feeding, and health inspections, these interventions are labor intensive and costly, and it’s not clear whether they’ve meaningfully reduced mortality rates.

Better Alternatives

Over time, new and potentially more effective technologies have been introduced for preventing and controlling lice, meaning that farmers have more options available to them. These include physical barrier systems that prevent lice from reaching salmons in the first place, methods that manipulate how deep salmons swim to avoid lice, and functional feeds designed to reduce lice infestations. Delousing lasers have also grown in popularity, with systems installed at more than 100 locations in Norway by 2024. The authors also note that some of these newer technologies may actually reduce the effectiveness of cleaner fishes when used together, further undermining the case for their continued use.

Changes In Regulation And Enforcement

In the 2020s, several changes to fish welfare regulation were made that applied to cleaner fishes, including mandatory reporting of violations. In response to these changes, SalMar, the second-largest salmon company in Norway, publicly announced that it would phase out the use of cleaner fishes due to the difficulty of meeting the new requirements. Furthermore, in 2024, the Norwegian Ministry of Agriculture and Food announced a target of 5% mortality for all farmed species, a threshold the authors describe as unachievable for cleaner fishes in the near future.

This article serves as a case study in what happens when an industry scales up an animal-based practice before adequate research is in place, and what it takes to reverse course. The authors are direct in their recommendations:

• The use of lumpfishes and wild-caught wrasses should be phased out by 2029.
• For farmed ballan wrasses, who some farmers consider more effective, the industry must meet all welfare requirements and demonstrate a 5% mortality rate by 2029, or discontinue their use.

For animal advocates, the case offers both a cautionary tale and a source of cautious optimism. Half a billion animals paid the price for an industry decision made without sufficient evidence. But the combination of growing welfare concerns, stricter regulatory enforcement, the availability of new technologies, and industry cost-effectiveness considerations ultimately drove a significant reduction in animal use, demonstrating that these levers, applied together, can work.