Aquawrasse: improving delousing behaviour and efficacy in farmed ballan wrasse

Project Summary


Ballan wrasse is one of the species used as cleanerfish in salmon farming. Their natural behaviour is to pick sea lice off salmon, providing a gentle and continuous method of ridding farmed fish of parasites. This project will study the wrasse’s personalities and behaviours to determine whether bolder wrasse are better at keeping salmon clean. The team will also explore the best and most comfortable conditions for Ballan wrasse to perform this role. The resulting knowledge can then be used to breed the most effective wrasse for use at sea. This will help reduce both the need for wild-caught wrasse and for alternative treatments. The project is an important milestone in the domestication and responsible use of Ballan wrasse for addressing the sea lice challenge in the UK and globally. 


Anticipated benefits

  • A better understanding of salmon delousing by Ballan wrasse, thanks to research into fish personality and interaction with farmed salmon. 
  • Improved husbandry practices during the hatchery phase and after deployment at sea, resulting in better fish health and welfare. 
  • Fewer wild-caught wrasse are needed due to the increased efficacy of farmed Ballan wrasse. 
  • Reduced need for pharmaceutical or mechanical sea lice treatments.


Industry Contribution


SAIC Contribution


Academia Contribution


  • Lead academic partner: University of Stirling 
  • Lead commercial partner: Loch Duart Ltd 
  • Commercial partner: Otter Ferry Seafish 


Cleaner fish are unique amongst farmed fish in that they are produced for their behaviour, so it makes sense that we focus our research on improving their natural instinct for delousing. While personality in fish is not a new concept, this is the first time it is applied to solve a real-world problem in aquaculture, and by working with nature we are aiming to improve the sustainability of cleaner fish as a method to control sea lice. - Dr Adam Brooker, Research Fellow, University of Stirling’s Institute of Aquaculture

It has long been thought that people’s personality traits determine how suited they might be to different types of jobs. This project takes the concept a step further by looking at how it might apply to a particular species of fish. The project team will undertake a series of tests to determine whether the boldness of individual Ballan wrasse makes them more adept at picking sea lice parasites from salmon.  

The researchers will study wild and farmed Ballan wrasse behaviour by introducing a new object into their tank and video-tracking individual cleaner fish. They will then monitor the wrasses’ reactions to the object – how quickly they interact with it – and correlate this with hatchery rearing conditions, acclimatisation protocols, and how they later perform when presented with the opportunity to clean salmon on actual fish farms. 

In addition to the personality study, the team will use hydroacoustic tracking, where underwater hydrophones are used to locate the position of tagged fish to understand and compare the behaviour (in terms of both delousing and interaction with salmon) of experienced wild wrasse and those produced in hatcheries. The same technique will be used to understand salmon behaviour by, for example, identifying whether the salmon swim closer to the wrasse and slow down in a bid to encourage them to clean. 

“Ballan wrasse are very special fish – they are very clever and demonstrate fantastic behaviour. If you walk by a tank, they will take an interest in you and physically watch you and follow. They are unique in many ways; each has their own personality and we want to correlate which traits – namely boldness and shyness – translate into Ballan wrasse being reliable and effective at delousing salmon.” Professor Herve Migaud, University of Stirling’s Institute of Aquaculture.

Drawing on a range of veterinary, rearing, and research skills, the project will also explore the optimal conditions for Ballan wrasse to perform their role across a range of variables, including their feed, the set-up and ‘furniture’ in pens, as well as the ratio of salmon to cleaner fish. 

“Wrasse have been an integral part of our production since 2014 and they have provided the business with a strong performance platform to grow salmon as naturally as possible. The natural behaviour of the wrasse isn’t taught, nor is it forced, but it is allowing the animal to express their natural behaviour in comfortable setting and under the full care of our site teams.” Lewis Bennett, Cleaner Fish Manager, Loch Duart