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Sea lice (Lepeophtheirus salmonis) are the biggest health challenge in Atlantic salmon production and a barrier to the Scottish Government’s strategy for the sustainable expansion of the industry. In the past decade, the use of cleaner fish to control sea lice has increased dramatically; they are now routinely used in all salmon farms in Scotland and are a vital component of integrated pest management strategies.

Research on cleaner fish over the last ten years has made significant progress to develop knowledge of the species’ biology and develop tools and methods to effectively farm both ballan wrasse and lumpfish. However, to truly reach their full potential as a sustainable biological sea lice control strategy, welfare concerns in farmed populations must be addressed and a consistently good delousing performance in salmon farms must be achieved. Industry requirements demand new research to address remaining bottlenecks to supply sufficient numbers of high-quality fish that are effective delousers.

Cleaner fish are produced for their delousing behaviour trait, and considerable gains in reliable delousing efficacy and an increase in the proportion of farmed populations that are effective delousers can be achieved by improving the behavioural quality of hatchery reared cleaner fish. This project will build upon the results from the previous SAIC ‘Aquawrasse’ project, which for the first time investigated variations in ballan wrasse behaviour phenotypes and their effect on delousing in salmon cages, and it will use this established baseline to inform and develop new methods that can be applied in a commercial setting. While sea lice foraging is a very difficult trait to phenotype in both experimental and commercial settings, the study of fish personality/coping style offers a proxy for delousing that could be used to select good cleaners in the ongoing domestication programme. More rapid gains in delousing efficacy could be achieved through environmental manipulations in the hatchery to exploit the natural plasticity of behavioural traits and produce farmed populations with a greater proportion of good delousers. In addition, the effect of ballan wrasse/lumpfish cohabitation on welfare and delousing efficacy has rarely been studied but is likely to have an impact on behaviour due to inter-species interactions and their different temperature and habitat preferences.

This research will have a high impact in the Scottish salmon farming sector and also in Norway where cleaner fish are also commonly used as more consistent delousing and a greater proportion of good delousers will result in fewer fish being deployed to maintain an effective therapeutic effect. This, combined with more effective health and welfare monitoring, will improve the ethical credentials and reduce the economic cost of cleaner fish as an effective sea lice management strategy.