Unlocking the secrets of secretions
Technique enables researchers to study substances from individual salmon lice instead of a group
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.
The research has resulted in the development of a new and precise way to collect and study secretory and excretory products (SEPs) from salmon lice (Lepeophtheirus salmonis). This includes substances released from the glands of the lice that make it easier for them to feed or evade their host’s immune system.
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 but these can be expensive, unreliable, and negatively impact animal welfare. Medicinal treatments can also have an impact on the environment and may only be used in small quantities.
Natural differences
Previous methods for extracting SEPs from salmon lice involved pooling together large numbers of individuals, which has the disadvantage of hiding the natural differences between individual lice. Those differences can provide a vital insight for developing targeted treatments or vaccines.
Understanding these secretions is an important step towards understanding louse biology and developing new, safe, and effective strategies for control.
The new method, as well as allowing study of individuals, also reduces the potential for louse faecal contamination. It enables collection of high-quality samples from a single louse per test, with substantial yields of secretory proteins per louse.
The research was led by PhD researcher Alexander Dindial alongside Professor James Bron and Dr Sean Monaghan at Stirling’s Institute of Aquaculture (IoA) in collaboration with Moredun Research Institute’s Kevin McLean.
“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,” said Dindial.
“Understanding these secretions is an important step towards understanding louse biology and developing new, safe, and effective strategies for control.”
State-of-the-art equipment
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 these could represent potential targets for vaccine development.
Wide variation between lice
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.
“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,” said Dindial.
“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.”
Building on earlier work
The work builds on a first-of-its-kind study led by Dindial and published last year that uncovered major differences in the secretions that the parasite uses to feed and evade the salmon immune system at different stages of its life cycle.
Investigation of a novel assay for the proteomic screening of the secretory and excretory products of individual salmon lice Lepeophtheirus salmonis was published in Veterinary Parasitology.
This work was funded by the East of Scotland Biosciences consortium as part of Dindial’s PhD studentship, with a funding contribution from Moredun Research Institute.
Collaborative research was conducted with the project Towards lice-resistant salmon: functional genetics and genome editing to enhance disease resistance in aquaculture, funded by UK Biotechnology and Biological Sciences Research Council (BBSRC), Sustainable Aquaculture Innovation Cluster and Benchmark Genetics Limited and involved partners from Roslin Institute at the University of Edinburgh, the Centre for Environment Fisheries and Aquaculture Science (CEFAS), Plymouth, the Atlantic Veterinary College at the University of Prince Edward Island, Canada, and Scottish steelhead trout producer Kames Fish Farming Ltd.
