I would like to thank Karol Orzechowski, Therese Larsen and Vegard Blindheim for your excellent feedback on this post.

Summary

Each year millions of cleaner fish are stocked in salmon farms to “clean” salmon of sea lice, leading to their suffering and death, without necessarily lowering the rates of sea lice. This post gives an overview of the issue in four parts: the neglectedness of fish welfare in general, the number of cleaner fish stocked in salmon farms and the reasons for this, the welfare issues cleaner fish endure, and suggestions for what can be done about this problem. Most data is from Norway, the world's largest producer of farmed salmon. Key takeaways: 

• Despite strong evidence for fishes' capacity to suffer, their welfare has long been neglected by both fishing industries and animal advocates.
• Sea lice is a big problem in salmonid farming, and after lice have become increasingly resistant to chemical treatment, other delousing methods have been employed, the least harmful to salmon of these being cleaner fish.
• Cleaner fish are not adapted to the environment that salmon live in and face disease and high mortality rates. There are also many problems with the way they are treated by the Norwegian cleaner fish and salmon industries.
• The evidence of cleaner fishes' effectiveness at delousing salmon is sparse, and it is argued that it is not adequate to justify the widespread use of cleaner fish.
• Suggested interventions are corporate outreach to improve cleaner fish welfare, or to end the use of cleaner fish entirely, as well as working on shifting the public opinions about fishes' welfare and moral value.

Introduction

The world’s appetite for fish products has been growing rapidly for the past couple of decades. Production of fish and other “seafood” is now over four times higher than it was in the 1960s, and the average global citizen today eats nearly twice the amount that they did then. Since 2013, more than half of all fish products has come from fish farms rather than wild-caught fishes. It is estimated that between 73 and 180 billion fishes live on farms each year, based on numbers from 2015. Many different species of fishes are being farmed, with carps being one of the most numerous. In Europe the dominant species are salmonids such as Atlantic salmon and rainbow trout, with an estimated 1,889 million individual Atlantic salmon and 470 million rainbow trout slaughtered globally in 2015, not counting the high numbers of fish that die before slaughter. These numbers are difficult to estimate as fish are killed in such high quantities, and fish are given such little moral consideration that slaughter data is recorded in tons rather than individual fishes.

These staggering numbers mean that fish are currently the most farmed vertebrate in the world, and the production of farmed fish is also projected to expand in all regions of the world in the future. This results in an enormous animal welfare issue, given that numerous studies have provided evidence that fish have the capacity to suffer both physically and emotionally. Not only can they feel pain and suffer in conditions such as low water quality, crowding, stressful handling, disease, and inability to display natural behaviors, but they can also learn from and remember painful experiences, which means they later experience stress and fear in similar situations. Despite this, fish welfare appears to be highly neglected both in the industry and, to a degree, in animal advocacy. Fish farming practices lag far behind what scientific evidence of fish sentience and needs would suggest are acceptable living conditions. Furthermore, few campaigns by animal charities have focused on fish welfare, although this is beginning to change.

Sea Lice In Salmonid Farming

In salmonid farming, a persistent issue has been parasitic infestation from sea lice, who feed on salmon and trout’s skin, causing severe scarring, infections, fin loss, and death if the number of lice is too high. In salmonid farms, fish are kept in open-net sea cages, where seawater flows freely through the cage. While this has its benefits, such as the natural removal of waste products and a steady supply of new water and oxygen, it also allows for pathogens and parasites, like sea lice, to enter the cages. The fish are stocked in densities that are far higher than that of any wild salmon population, allowing the lice to propagate to high levels. This can in turn allow louse larvae to spread from the cages to wild salmon, who also become infected with the parasite; in some cases, this has led to a dramatic fall in local wild salmon populations. A lot of effort has therefore been put into controlling the parasite and keeping the infestation levels low.

In Norway — the world’s largest producer of farmed salmon with a production of 212 million salmon per year — the industry spent over 5 billion Norwegian kroner (roughly 550 million USD) on sea lice control in 2015, and this number has likely risen since. Chemical treatments to control lice infections have been a dominant strategy for decades, but in the past couple of years, their use has dropped due to the sea lice developing resistance to most of the active compounds. In order to keep lice levels low, the industry has therefore had to shift rapidly to new control efforts, often without having good evidence for their effectiveness or adequate knowledge of their effects on fish welfare before using them. Thermal delousing is a method where the salmon are placed in warm water for 30 seconds, which is thought to cause the fish considerable amounts of pain, and can cause panic behavior and cerebral and palate hemorrhage (bleeding in the brain and roof of the mouth), but most salmon survive the treatment. Mechanical delousing is another method, where the salmon are flushed with water and sometimes brushed to remove the lice, which can cause damage to their skin. A method that has received fewer reports of mortalities, but which also risks resistance is putting the salmon in freshwater to kill the lice. 

A final delousing method is the use of cleaner fish. “Cleaner fish” is an umbrella term for different species of fish, most commonly lumpfish and different types of wrasses, that feed on sea lice from salmon’s skin, “cleaning” them from the infestation. Cleaner fish are, in other words, fishes that are used in fish farming, not to produce food but to control parasites on other fish. If this sounds unique, it is: cleaner fish are “likely the only case of a vertebrate being deployed to control parasites on another vertebrate in a commercial setting.” 

In the past couple of years, the use of cleaner fish has increased sharply, and today around 60 million cleaner fish are stocked in salmonid farms globally each year. In Norway alone, 49 million cleaner fish were stocked in 2018. To keep up with this high demand, cleaner fish are both caught wild and bred in farms. Compared to other delousing methods, cleaner fish are less stressful to salmon, and consumers of salmon may also view this “natural” method as preferable to chemical treatment. However, the use of cleaner fish comes with huge welfare issues, and to date, there is not enough scientific evidence of their effectiveness in louse control to justify their use on such a massive scale. 

Cleaner Fish Welfare Issues

There have been concerns about the welfare of cleaner fish from many different actors for a long time. The Institute of Marine Research published a risk report in 2019, where they assessed the risk of poor welfare for cleaner fish as “high.” This is because cleaner fish have different needs and are adapted to different water temperatures and water flow than what salmon are adapted to. When put into salmon farms, they are therefore put in an environment they are not adapted to and suffer as a consequence. Disease is also a big risk factor: in 2018-2019, the Norwegian Food Safety Authority supervised a selection of salmon farms, cleaner fish farms, and fishers who catch wild cleaner fish in Norway to learn about the state of cleaner fish welfare in the industry. They found that on average, 40% of cleaner fish in salmon farms are found and reported dead and that many of the remaining 60% disappear: it is thought that some escape, some dissolve before being reported, and some are eaten by the salmon, who are carnivorous. Another study found that mortality was sometimes up to 100%, and wrasse had a mortality spike right after being stocked in the sea cages.

Further, in their investigations, the Food Safety Authorities found that 28% of salmon farm sites and 64% of cleaner fish farm sites had at least one deviation from the rules that apply to cleaner fish keeping. At cleaner fish farm sites the most common deviations were related to vaccination of fish and failure to implement measures when mortality rose above normal. Around half of the sites did not give lumpfish anesthetics before vaccination, claiming that it was unnecessary and led to worse welfare for the fish due to excessive handling, which is stressful for the fish. However, the industry failed to provide scientific documentation that anesthesia was not necessary to avoid pain and fear for the lumpfish. Given the thickness of the needle relative to the fish’s body size, it is likely that vaccination is a very painful experience without anesthetics. In addition, there was uncertainty in the industry related to how soon the fish could be moved to sea cages after being vaccinated, and in cases where they are moved too early, they may contract diseases before immunization from the vaccination was complete. They also found that the sites didn’t have good systems for controlling water quality or recording mortality rates, which in many cases led to a failure to implement measures to solve these problems. 

At salmon farm sites, the most common problems were failure to remove cleaner fish from cages before mechanical delousing of the salmon, failure to record how many cleaner fish were left alive after salmon were sent to slaughter, and failure to implement measures when mortality rose above normal. Cleaner fish do not get infested with sea lice, and therefore do not need to be deloused. Delousing causes heightened mortality among the fish, and farmers are therefore required to remove cleaner fish from the cages before delousing the salmon. This is a rather difficult job, and many sites, therefore, don’t do this at all, or not well enough, resulting in a number of cleaner fish being harmed or killed by the procedure. The failure to report the number of surviving cleaner fish after salmon are sent to slaughter is problematic as it makes it difficult to estimate how many cleaner fish have died or disappeared. Finally, many sites don’t have processes for solving problems related to high mortality rates of cleaner fish. Some sites have extremely high tolerances for cleaner fish mortalities and did not register heightened mortality before it reached 75%. 

Evidence Of Effectiveness

The evidence for cleaner fishes’ effectiveness as louse control is sparse. In one analysis, it was found that only 6% of sites were able to avoid other delousing methods entirely by stocking cleaner fish. They also found that cleaner fish use was not correlated with louse levels, however, it is uncertain whether this was because of a weak effect of cleaner fish on louse levels, or that sites with higher infestation levels stocked more cleaner fish to solve the issue. It was found that by stocking cleaner fish early there was a small but significant increase in how long the site could wait before using other methods of delousing. However, both this analysis and other studies have said the effects were very variable, weak overall, and lasting only for a short time. 

Meanwhile, a review by Overton and colleagues found efficacies ranging from a 28% increase to a 100% reduction in lice numbers. The effects increased with the number of cleaner fish stocked, but only the sites with the very most cleaner fish didn’t have a positive louse population growth, according to Barrett and colleagues. Overall, the evidence base for cleaner fish is not solid enough, and too few studies have been done in large sea cages that are representative of the environment that cleaner fish are actually used in the industry. The evidence available today suggests that controlling lice levels using cleaner fish is not markedly better than other delousing methods, and both the reviews conclude that the evidence is not proportional to the scale at which cleaner fish are used to combat sea lice. The high mortality rates and evidence of poor welfare should therefore make the use of 60 million cleaner fish globally each year completely unacceptable and unjustifiable. 

What Can Animal Advocates Do?

The welfare issues with using cleaner fish are various and widespread, and it is clear that much more should be done to reduce their suffering. Fortunately, it seems that there are things that can be done to improve the welfare of cleaner fish. In the near-term, it should be in producers of salmon’s interests to improve the welfare of cleaner fish and lower mortality rates: the effectiveness of cleaner fish on sea lice control is dependent on their welfare, and the high losses not only reduce the effectiveness of the cleaner fish on lice levels, but also increases expenses when new cleaner fish need to be stocked to replace the dead. In Washington State, Canada, and the E.U., there is a movement towards prohibition of open-net sea cages due to their damaging effects on the environment; Norway (which is not part of the E.U.) has also begun trying out land-based or closed containment sea cages in addition to open-net sea cages. These farming systems eliminate the need for cleaner fish, as sea lice are no longer an issue. In Norway, cleaner fish are protected under the Animal Welfare Act, which protects them from “unnecessary stresses and strains” and only allows the keeping of animals if they are kept in environments that “provide good welfare based on species-specific and individual needs” and “promote good health and contribute to security and well-being”. While it may appear obvious that keeping cleaner fish as it’s done today is in violation of this law, the problem may lie in what are perceived as “necessary” and “unnecessary” stresses and strains.

Given the above, it seems that a variety of interventions may be promising for improving cleaner fish welfare. To improve the lives of the cleaner fish who are used in salmon farming, corporate outreach may be a particularly promising intervention, as it has a relatively strong evidence base and track-record for other animals; it should be in producers’ interests to improve cleaner fish welfare, even if their only goal is to increase the profitability of salmon farming. On the production side, there are a number of things that can be done to improve cleaner fish welfare, such as changing from feeding with pellets to using feed blocks, and making use of operational welfare indicators that have been developed based on scientific research on cleaner fish needs. However, it is unclear whether corporate campaigns for fish welfare will be as effective as they have been for other animals, because their likeliness of being accepted by corporations beyond what is profitable for them depends on public support, which may be weaker for fish. 

The salmon industry and the authorities in Norway have developed an attitude that accepts high losses of cleaner fish, and seems to view cleaner fish as less valuable than salmon, as they are not a product to eventually be sold for profit. The Norwegian Food Safety Authority notes that the level of suffering that can be accepted as necessary or not depends on society’s attitudes and scientific knowledge. Therefore, in order to make corporate campaigns effective, work also has to be done on shifting public opinions on fish’s welfare and moral value. Generally, it seems that fish receive less concern from consumers about their welfare than other farmed animals. However, one study from Norway found that consumers of farmed fish were willing to pay more for higher-welfare fish, suggesting that there may be hope for shifting attitudes towards caring more about fish welfare. Cleaner fish may be seen by consumers as a “natural” way to improve salmon health and welfare, however, so it is important to be clear about the many problems associated with their use. 

Other than focusing on improving the welfare of cleaner fish, efforts should be made to end the use of cleaner fish in salmon farming. It may be that good welfare for cleaner fish in salmon farms is unachievable because of the differences in their needs, and the evidence to date does not support cleaner fish as an effective control effort against sea lice. Here, too, corporate outreach and work on shifting public opinions seem promising. 

To conclude, the use of cleaner fish is today a completely unjustifiable practice that leads to the suffering and death of millions of cleaner fish each year. Despite this, the use of cleaner fish has been rapidly growing and relatively little work has been done to reduce their suffering compared to other farmed animals. It seems like interventions that have worked for other animals in the past, such as shifting public opinions and conducting corporate outreach, can be promising for reducing the suffering of cleaner fish in salmon farms, and eventually ending their use entirely.