Improving the performance of cleaner fish in salmon aquaculture

A new project aims to produce ballan wrasse that are more effective at eating sea lice on salmon farms.

Ballan wrasse - which are used to remove sea lice from salmon in marine net pens - are farmed in Scotland by Mowi and Otter Ferry Seafish. Photo: SAIC

The project builds on more than 10 years of ballan wrasse research led by the University of Stirling’s Institute of Aquaculture and will explore a range of nutritional and environmental factors, such as the formulation of feeds and rearing conditions, to determine how they impact the health and welfare of the cleaner fish species.

Otter Ferry Seafish, BioMar, Scottish Sea Farms, Mowi, and the Sustainable Aquaculture Innovation Centre (SAIC) are supporting the research, which could improve the robustness, welfare and resilience of ballan wrasse when deployed into salmon pens and enhance their ability to deal with sea lice parasites.

Scientists believe hatchery processes during their early development may not only impact on their performance and welfare, but also their ability to become effective delousers at sea. Determining the optimal conditions – particularly as they grow in hatcheries – could be transformational for the sector’s approach to sea lice treatment.

Ballan wrasse display complex behavioural traits throughout their lifecycle, culminating in their sea lice foraging activity. Scientists believe hatchery processes during their early development may not only impact on their performance and welfare, but also their ability to become effective delousers at sea. Determining the optimal conditions – particularly as they grow in hatcheries – could be transformational for the sector’s approach to sea lice treatment.

The outcomes of the research project could be used to scale up hatchery production. Ballan wrasse are already used widely by the aquaculture sector; but current levels of demand outstrip the supply coming from hatcheries, with around four cleaner fish per 100 salmon being optimal.

Professor Herve Migaud from the University of Stirling’s Institute of Aquaculture said: “Years of research have taught us that ballan wrasse are a complex fish species. Their behaviour can be significantly impacted by environmental factors from a very early developmental stage including the nutrients they are given, especially as they have a rudimentary digestive system without any stomach.

“In the wild, it can be a case of survival of the fittest, and the fish tend to develop a level of resilience that we are aiming to understand and recreate in a controlled environment. Exploring the impact of different variables in the hatchery process, in particular, can help us to create the best possible conditions to help the fish thrive and prepare them for when they are deployed into a salmon farm.

“The demand for cleaner fish is growing and the aim is to get to a point where we can meet the demand for healthy and effective hatchery-reared ballan wrasse and enable the sector to reach full reliance on farmed rather than wild cleaner fish in coming years, ultimately helping salmon farmers with a sustainable solution to sea lice.”

Researchers will also look at the nutrients in the feeds, such as vitamins and minerals, needed by ballan wrasse from the first feeding and weaning stages to support bone and cartilage health and minimise the risk of deformities, exploring the use of supplements, immunostimulants and functional feeds to improve resistance to bacterial disease. These will help to better prepare ballan wrasse for what they experience in the waters of a fish farm.

Anticipated benefits of the project include new guidelines for increased survival, welfare and robustness of farmed ballan wrasse in hatcheries as well as increased efficacy of delousing programmes, which could lead to a reduction in medicinal treatments. There is also potential to create new feed products for use in hatcheries.

Heather Jones, CEO at SAIC, said: “The project builds on years of valuable cleaner fish studies and is a prime example of how innovation and collaboration can help solve challenges in new ways, for the benefit of the entire sector. Determining the best conditions for ballan wrasse, and communicating the results and recommendations across the aquaculture sector and supply chain, could lead to significant progress in the collective efforts to tackle sea lice sustainably.”

Dr. Antonios Chalaris, product manager at BioMar, added: “Nutrition is a major contributor to the performance and well-being of ballan wrasse. Over the last decade we have invested significantly in research to develop recipes that are tailor-made for the specific requirements of ballan wrasse, including our mild-extruded Symbio products which are already successfully being used in hatchery production and deployment. Gaining a deeper understanding of the needs of the species will provide valuable insights to help refine and fine-tune feed ingredients to support the fish to grow and thrive.”

Dr. Thomas Cavrois-Rogacki, research and development and health manager at Otter Ferry Seafish, added: “Improving the performance and welfare of the ballan wrasse at the hatchery is one of the keys to unlocking the full potential of the species as cleaner fish. While early research on the species focused on increasing the numbers of fish produced, now is the time to focus on improving their quality, which is unconditionally linked to their ability to delouse and their resilience at sea. Furthermore, the expansion of the ballan wrasse culture has the potential to create new jobs in rural areas to support hatchery production and deployment at sea and to promote an eco-friendly, efficient and cost-effective approach to tackling sea lice.”