New case study: Aquawrasse - understanding wrasse behaviour to improve salmon health

Studying wrasse personality and behaviours to determine whether bolder wrasse are better at keeping salmon clean

Ballan wrasse are used in salmon farming as ‘cleaner fish’, naturally removing sea lice from salmon - a major health challenge for the industry. This project explored whether personality traits, such as boldness, influence how effective wrasse are at delousing, and how farming conditions can support their natural behaviour.

The project partners were the University of Stirling, Otter Ferry Seafish and Loch Duart, and the total project value was £199,170.

Cleaner fish are unique because they are farmed for their behaviour rather than for food. As the sector moves away from wild-caught wrasse toward farmed production, understanding and preserving traits that make them good cleaners is essential. Researchers compared wild and farmed wrasse at a commercial sea farm, using behavioural tests and acoustic tagging to monitor activity.

Results showed clear personality differences: wild wrasse were generally more proactive, while farmed wrasse were more reactive - likely due to uniform hatchery environments. These findings suggest personality is influenced by both genetics and rearing conditions, meaning selective breeding and environmental enrichment could improve farmed wrasse performance.

The study also revealed that salmon modify their behaviour during interactions, slowing down when wrasse approach, indicating a mutual relationship rather than one-sided exploitation.

Future work will focus on identifying desirable personality traits for breeding and refining hatchery practices, e.g., varied feeding regimes and environmental enrichment, to produce wrasse that are more effective at controlling sea lice. This research is a step toward sustainable, welfare-friendly solutions for salmon farming.

The full name of this project is ‘Aquawrasse: improving delousing behaviour and efficacy in farmed ballan wrasse’.

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