New case study: scaling up production and implementation of farmed cleaner fish

Scaling up Ballan wrasse production by domesticating the species and optimising breeding, nutrition, health and welfare.

Sea lice are a challenge for salmon farming, with cleaner fish such as Ballan wrasse (and to a lesser extent, lumpfish) used as part of pest management strategies - these species naturally remove lice from salmon, reducing reliance on medicines. However, Ballan wrasse can be difficult to rear in captivity, requiring research to optimise breeding, nutrition, health management, and deployment.

This project sought to scale up Ballan wrasse production by domesticating the species and improving broodstock management, larval rearing, nutritional protocols, disease control, and welfare. Valued at £4.1m, the partners were Mowi Scotland, Scottish Sea Farms, BioMar. Otter Ferry Seafish and SAIC.

Four work packages focused on:

• Breeding: developed methods to extend spawning seasons, increase the number of males (essential for reproduction), and improve egg quality. They also created genetic tools for selective breeding and achieved a world first - breeding the first generation of Ballan wrasse entirely in captivity.
• Nutrition: feeding protocols for young wrasse, including live feed enrichment and weaning strategies, to reduce deformities and support healthy growth.
• Health: tackled bacterial infections, particularly furunculosis, by developing and testing an effective vaccine. Researchers also studied egg microbiota to manage disease transmission.
• Deployment: using acoustic tracking technology, the team studied wrasse behaviour in salmon pens to optimise conditions for their natural lice-removal behaviour and compared them with lumpfish (another type of cleaner fish).

The project developed new breeding, feeding, and health protocols, alongside best-practice guidelines for deployment. It also introduced tools for genetic improvement and validated products like wrasse feed blocks and hides. These advances make large-scale, sustainable production of Ballan wrasse possible, improving their effectiveness as cleaner fish and reducing reliance on medicines. The achievement of captive breeding opens the door to selective breeding for even better performance. The project won the Applied Research Award at the Aquaculture Awards 2019.

Read the case study