Stirling team develops precise new method to analyse secretions from individual salmon lice. A University of Stirling study could pave the way for the more efficient study of the secretions that salmon lice use to avoid fish defences, potentially enabling the development of new strategies to protect salmon from infestations.

Salmon lice feed on the skin, mucus, and blood of fish, causing open wounds that can lead to infection – reducing the market value of farmed fish and increasing the chance of secondary infections.

Various treatments have been developed to tackle sea lice infestations in Atlantic salmon aquaculture – which costs the industry more than $1b a year – but some of these can be expensive, unreliable, environmentally damaging, and negatively impact animal welfare.

Previous methods for extracting SEPs from salmon lice involved pooling together large numbers of individuals, hiding the natural differences between individual lice, which can provide a vital insight for developing targeted treatments or vaccines.

The new method, as well as allowing study of individuals, also reduces the potential for louse faecal contamination. It allows collection of high-quality samples from a single louse per test, with substantial yields of secretory proteins per louse.

Mr Dindial explained:

“Salmon lice cause hundreds of millions of pounds of damage annually to the global salmon aquaculture industry through mortality, lost production and the implementation of control measures. Understanding these secretions is an important step towards understanding louse biology and developing new, safe, and effective strategies for control.”

Research involved collecting secretions from individual salmon lice by placing a small drop of solution over their mouths and letting them release proteins into it. These proteins were then examined using a technique called liquid chromatography tandem mass spectrometry to analyse the exact protein composition of each of the samples. This technique uses state-of-the-art equipment to separate the components of a sample, breaking it into fragments and analysing them – revealing protein composition and helping to identify them.

The team found 148 total secretory proteins, 64 of which were detected in each of the tested conditions – some of which could represent potential targets for vaccine development.

The secretory protein profiles of individual lice showed a wide variation in protein number and diversity, a pattern consistent with other ectoparasites like ticks and mosquitoes.

Mr Dindial continued: “This work has the potential to expand our knowledge of salmon louse biology and to provide insight into louse proteins that could be exploited to help fish mount an immune response against infection.

“The novel methodology developed here has the potential to directly facilitate further research into salmon louse secretory biology. It allows for the reproducible, reliable, and efficient extraction of high concentrations of salmon louse secretions, all while minimising faecal contamination.

“As well as improving the study of these secretions, the protocol could be used to investigate how drug or therapeutic treatments might alter louse secretory activity, ultimately advancing efforts to control this parasite.”

The work builds on a first-of-its-kind study led by Mr Dindial, published last year, that uncovered major differences in the secretions that the parasite uses to feed and evade the immune system at different stages of its life cycle.

Image: Alexander Dindial