Cleaner fish should be phased out if adequate animal welfare cannot be documented, researchers say

The study is a collaboration between researchers from Deakin University in Australia, the Institute of Marine Research, and the Norwegian Veterinary Institute.

“Cleaner fish were introduced on a large scale based on an insufficient level of knowledge, after small-scale trials showed promising results. The focus was on reducing lice on salmon, and therefore, too little consideration was given to the welfare of the cleaner fish,” says researcher Frode Oppedal from the Institute of Marine Research.

“In the late 1980s, wild-caught cleaner fish were introduced and became common in salmon farming,” he explains.

At that time, problems with salmon lice on farmed salmon increased, at the same time as salmon lice developed resistance to delousing chemicals.

“It was then tested whether Norwegian wrasse would pick lice directly off the salmon, since it was known from other countries that similar fish could remove parasites from other species. Apparently, this seemed to work very well,” Oppedal says.

From 2012, a new cleaner fish, the lumpfish, was introduced, followed by extensive farming and deployment in sea cages.

Over the past decade, approximately half a billion wild-caught and farmed cleaner fish have been released into Norwegian sea cages.

Poor welfare in aquaculture facilities

“Many believed that cleaner fish largely removed salmon lice from farmed salmon,” says Kathy Overton, lead author from Deakin University.

In the years following the introduction of cleaner fish, research has shown that they are far from being the effective lice eaters many believed.

“Several studies have shown that only a small proportion of cleaner fish actually eat lice, and that the effect varies greatly between species, locations, and environmental conditions,” Overton says.

At the same time, it has been documented that cleaner fish have poor welfare in sea cages.

“There is consistently documented high mortality or loss of these fish,” says Kristine Gismervik, head of animal welfare at the Norwegian Veterinary Institute.

She states that production conditions in salmon sea cages are often not adapted to the physiology and needs of cleaner fish.

“We see that disease, handling, and environmental stress are key causes of the poor welfare,” Gismervik says.

Fewer cleaner fish are used now than before

From 2008 to 2019, the use of cleaner fish increased year by year.

The growth was due to a lack of alternative methods and the collapse of cod farming. This led many vacant marine hatchery facilities to switch to producing cleaner fish.

In the peak year 2019, more than 61 million cleaner fish were released. Since then, the number has declined, and by 2024, it had been reduced to 22.5 million.

The reason for this decline is partly that new and more effective delousing methods have been developed, that the lice-eating effect is low, and that there has been increased focus on the welfare of cleaner fish in aquaculture facilities.

Stricter animal welfare regulations, mandatory sorting before treatment, and increased enforcement by authorities have also made the use of cleaner fish more demanding.

Several major industry players have already stopped using cleaner fish.

Researchers want to phase out the use of cleaner fish

The research group behind the new publication is clear that the aquaculture industry should stop using cleaner fish. In the article, they conclude the following:

• Lumpfish should be phased out by 2029.
   
• Wild-caught wrasse should be phased out by 2029.
   
• If farmed ballan wrasse is to be used, the industry must clearly document its effectiveness at full scale and, simultaneously, reduce mortality to 5 per cent by 2029. According to the researchers’ knowledge base, it is unlikely that these requirements can be met.

Read the full article: The rise and fall of cleaner fish use in Norwegian salmon farming