Wrasse the way to do it

Cleaner fish welfare is increasingly an issue on the scientific and policy agenda for aquaculture

A team of UK researchers has received funding to find better ways to vaccinate ballan wrasse against bacterial infection.

It is hoped the project could help to grow the use of wrasse as cleaner fish to control sea lice on salmon farms.

The consortium – led by the University of Stirling’s Institute of Aquaculture and the salmon producer Mowi, with support from Otter Ferry Seafish, Ceva Ridgeway Biologicals and the Sustainable Aquaculture Innovation Centre (SAIC) – will explore the range of factors that determine the best possible conditions for delivering vaccinations against Aeromonas salmonicida, a bacterium which can cause potentially fatal outbreaks of disease in cleaner fish.

Ballan wrasse currently receive vaccinations against multiple health conditions at the hatchery stage. However, the group will look at alternative formulations of the vaccine, which could offer greater protection against disease. A core aim of the project is to determine the most effective composition of antigens to elicit the best immune response in juvenile fish.

The team will also consider the best timing and method of delivering the vaccine – ideally through immersion which can be easier to administer than injections – and assess and compare the way ballan wrasse react to each variable.

Wrasse at Otter Ferry

Dr Sean Monaghan, of the Institute of Aquaculture at the University of Stirling, said: “Enhancing vaccines for Aeromonas salmonicida could represent a significant step forward in the use of ballan wrasse in aquaculture. We know that prevention is better than cure and we are, therefore, working towards the development of more effective vaccine formulations and protocols that can be used by hatcheries and producers to improve fish welfare.”

Dougie Hunter, technical director at Mowi, said: “Ballan wrasse, alongside lumpfish, are excellent cleaner fish and a natural solution to effectively manage sea lice on our salmon. For us to give these fish the best environment and welfare, we must protect them against stress and disease, including infection caused by Aeromonas salmonicida, which can be observed in wrasse from an early stage.

“At Mowi we are committed to ensuring the best fish welfare at all our facilities and for our new cleaner fish hatchery in Anglesey, and that includes proven disease prevention tools such as vaccines. Mowi’s collaboration with Scotland’s leading fish health and vaccine experts and SAIC will be vital in finding the best vaccination strategies to enhance wrasse health protection.”

Heather Jones, CEO at SAIC, said: “Fish health and welfare is an ongoing focus for the sector, so we are pleased to extend our commitment to this collaborative project and help the valuable research to progress. Formulating a vaccine that enhances wrasse health protection will ultimately support the use of this sustainable sea lice treatment which could unlock further economic growth for the wider aquaculture sector.”

Ballan wrasse

Better protection
Meanwhile, over the past few years, awareness has been growing that salmon farmers need to take account of cleaner fish health and welfare as well. This month, as from 19 May, the RSPCA’s revised welfare standards for Atlantic salmon come into effect, including a raft of new standards specifically concerning cleaner fish welfare.

An important new requirement is that cleaner fish must be removed from the crowd in a pen before the salmon are removed for treatment, for example delousing. It has been found that some treatment systems designed for larger fish such as salmon can be problematic for smaller cleaner fish, especially lumpfish, which have a tendency to cling onto flat surfaces and can end up being stuck in pipes and filters.

The revised standards state that any dead cleaner fish must be removed promptly and advises that this should be carried out at least twice a week, and preferably daily.

By 1 May 2025, cleaner fish must be removed from the crowd or prevented from participating in the crowd prior to any salmon handling event that requires the fish to be removed from the pen environment.

Cleaner fish must not be exposed to any non-medicinal treatment that will cause injury or suffering, and a risk assessment must be carried out.

When cleaner fish need to be despatched, only humane methods may be used. These are defined as (a) being put into an anaesthetic overdose under veterinary prescription; or (b) a percussive blow or electrical stun-to-kill, for wrasse over 50g. Other slaughter methods such as bleeding (without stunning), chilling/freezing or asphyxiation are not permitted.

The standard calls for the use of vaccination where necessary and sets out rules for how that is to be carried out. It also sets out parameters on stocking density and requires that cleaner fish mortalities, and the causes, are recorded.

Sean Black, Senior Scientific Officer and aquaculture specialist at the RSPCA, said: “The new farmed Atlantic salmon standards will be a huge step forward for fish welfare… we are pleased to introduce over 80 new standards to improve cleaner fish welfare. These include the need to risk assess the impact of treatments on their welfare, the requirement to record, categorise and monitor all mortality causes and reduce transport stocking density.”

Lumpfish

Glowing report
Lumpfish can play an important role in helping to keep lice numbers down, but did you know they can glow in the dark?

A study led by Thomas Duhasz-Dora of University College, Cork, Biofluorescent response in lumpfish Cyclopterus lumpus to a therapeutic stressor as assessed by hyperspectral imaging, looked into whether the fish’s  natural bioluminescence was affected by external environmental factors – specifically, stress.

Lumpfish have been found to emit green and red biofluorescence within the blue shifted light of their environment. The researchers measured the bioluminescence following a freshwater bath treatment that mirrors a typical non-medicinal treatment for, to give an example, amoebic gill disease (AGD).

The study found that the treatment, which is mildly stressful for the fish, was associated with an increase in luminescence as detected by hyperspectral imaging. This suggests, the researchers say, that such analysis can be used as a non-invasive test for stress.

Further, the study found that this stress reaction was not displayed equally between individuals – raising the prospect that strains of lumpfish with greater tolerance of stress could be raised.