The salmon aquaculture industry has adopted the use of invertivorous ‘cleaner fishes’ (CF) for biological control of sea louse infestations on farmed salmon.

A national scale database of louse counts was used for this study, delousing treatments and cleaner fishes stocking events on Norwegian salmon farms to test for evidence of cleaner fishes efficacy at 488 sites that completed a grow-out cycle within 2016–2018.

The analysis revealed that sites using more cleaner fishes over the duration of a grow-out cycle did not have fewer lice on average, likely because cleaner fishes use is reactive and in proportion to the scale of the louse problem.

A better understanding of factors affecting cleaner fishes efficacy in commercial sea cages is required to inform legislation and drive more efficient and ethical use of cleaner fishes by the salmon aquaculture industry.
 

Highlights

• The use of cleaner fish was not correlated with sea louse infestation density.
• Farms that used many cleaner fish were able to wait longer before delousing.
• Stocking cleaner fish slowed sea louse population growth over the next 12 weeks.
• Effects were highly variable, resulting in weak effects when viewed at a national scale.