New case study: improving cleaner fish performance in salmon farming

Exploring the behavioural aspects of cleaner fish for improving delousing efficacy

Control of sea lice presents a health challenge for Atlantic salmon farming. In response, the use of cleaner fish – particularly ballan wrasse and (recently to a much lesser degree) lumpfish – has become widespread, forming a part of integrated pest management strategies. The reliance on wild-caught cleaner fish is not sustainable, highlighting the need for a viable, farmed alternative.

While industry efforts have focused on production and health, research funded by SAIC through the ‘CleanGain’ and ‘HEIDI’ projects explores how behaviour and welfare can boost delousing success. Valued at £394k, the partners were Otter Ferry Seafish, University of Stirling, Swansea University, VisiFish, Loch Duart, Bakkafrost Scotland, Mowi Scotland and RSPCA. .

The studies examined how genetics, rearing conditions, and personality traits influence cleaner fish performance, and how hatchery practices and cohabitation strategies can be optimised. Four areas were investigated:

1. Behavioural profiling: researchers identified consistent personality traits - boldness, anxiety, and sociability - linked to delousing behaviour. Lumpfish were generally bolder and more sociable than wrasse. Simple tests, such as measuring how quickly fish leave shelter, could help select individuals better suited for lice removal, supporting future breeding and deployment strategies.
2. Welfare assessment via imaging: photographic analysis proved a reliable, non-invasive way to assess body condition, outperforming AI-based video measurements, which struggled with accuracy due to angle and quality issues. This highlights the potential for practical welfare monitoring in hatcheries.
3. Cohabitation effects: housing lumpfish with wrasse reduced their exploratory behaviour but did not increase aggression in either species. These findings suggest mixed-species stocking poses minimal risk of conflict, informing husbandry decisions that balance welfare and performance.
4. Hatchery enrichment: early results show that adding natural features like kelp hides encourages more active, natural behaviours in wrasse compared to standard bare tanks. This could improve adaptation to sea pens and enhance delousing effectiveness.

Behavioural screening and selective breeding could improve lice removal by up to 20%, saving an estimated £5 million annually. Tools like VisiFish AI offer promise for automated assessments, though refinement is needed. Continued investment from salmon producers is critical to realise these benefits.

The full title of this project is ‘Optimising cleanerfish performance: behavioural, welfare and hatchery innovations for sea lice control’.

Read the case study