October 26,  2020

 

Nofima: Drawing on natural abilities of Pacific salmon to fight sea lice

 
 

Researchers will use the gene editing tool CRISPR-Cas9 to study the genes of Pacific salmon and their resilience against sea lice, Nofima said.

 

Sea lice are naturally occurring parasites that attach to and feed on salmon. Infestation of Norwegian salmon farms is common and severely affects the welfare of fish if unchecked.

 

Hence, Nofima researchers, along with partners from the United Kingdom, the United States, Canada, Sweden and Australia, are aiming to apply CRISPR-Cas9 in a way that could make farmed salmon an unattractive host for sea lice. The new project is supported by funding from the Norwegian Seafood Research Fund (FHF).

 

Existing methods for preventing lice infestation are not entirely effective. Lice wound and stress the fish, and this can lead to death if left untreated. The most effective methods of treatment, such as mechanical de-lousing, can also substantially cause stress.

 

Furthermore, common therapeutics can be damaging to wild ecosystems, and lice frequently develop drug resistance making the treatments less effective. The aquaculture industry is therefore looking for an environmentally friendly solution that can effectively limit lice attachment with little to no negative impacts on fish welfare, Nofima said.

 

Research has shown that several species of Pacific salmon are unattractive as hosts for sea lice. Detailed research is needed to uncover the genetic basis for these differences and to see if this knowledge can be utilised in a way that helps prevent sea lice infestation among farmed Atlantic salmon.

 

"It is no exaggeration that the knowledge we create in this new project could transform the Norwegian aquaculture industry if Atlantic salmon can be made to be highly or completely resistant to lice," said senior researcher and project leader Nick Robinson of Nofima.

 

Differences in the genetic code make Atlantic salmon more attractive hosts to lice than coho or pink salmon. Such differences, for example, could result in the production of chemical attractants by Atlantic salmon but not by coho, or result in an effective defensive response of the salmon skin to newly-attached lice in pink salmon but not in Atlantic salmon.

 

As such, the research aims to find the genetic basis for these differences between Atlantic and North American salmon species.

 

"If we can reveal the differences in the genetic code that cause lice to be attracted to Atlantic salmon, or that makes the skin of North American salmon a bad place for sea lice to settle and develop, then it may be possible for us to use that information to make Atlantic salmon resistant to sea lice and have better health," said Robinson.

 

CRISPR-Cas9 is a tool that enables making targeted changes to the genetic code. However, the researchers need to first determine which genes could be edited to have a desired effect, and later, making the desired edits.

 

"CRISPR-Cas9 is still a relatively new technology in the aquaculture research, but can allow for very precise and targeted changes at specific genes in the salmon genome known to be involved in cross-species variation in resistance to lice and the success of its use depends on the type of change that is needed and on the position and code of the gene to be edited," said Professor Ross Houston of the Roslin Institute UK whose team will work closely with Nofima on this and other parts of the project.

 

The researchers will find and measure the chemical components that each salmon species releases. Then they will test how sea lice react to each of the unique chemicals released by Atlantic salmon and reveal which of them are semiochemicals that can attract or repel lice.

 

"We can observe whether lice are excited and stimulated to swim towards these chemicals," said Howard Browman of the Institute of Marine Research in Norway.

 

The researchers will also undertake experiments to study the response to attached lice by different cell types in the salmon skin and how this response differs in the resistant North American species.

 

Finally, the researchers will determine what genes are affecting the production of these semiochemicals and affecting the response of different cells in the skin and test how these genes can be "disrupted" using CRISPR-Cas9 to make Atlantic salmon unattractive to lice.

 

If the researchers succeed in carrying out gene editing, the salmon must be thoroughly tested up to adult size in closed facilities to investigate how effective the change is and reveal any potential unwanted side effects. Robinson emphasised that this project will not make genetically edited fish available to industry and that further testing will be needed.

 

They will also consider the risks of sea lice adapting to the changes in the salmon, and how this would be best prevented.

 

"Lice adapt to become resistant to chemical treatments, and we need to consider if they might adapt to overcome any specific changes that are made to Atlantic salmon" said Tim Dempster from the University of Melbourne, Australia.

 

Additionally, the project will consider possible effects on wild salmon populations.

 

"In the project, we will determine how the changes would be best implemented in a farming population, to make all Norwegian farmed salmon resistant to lice", said Robinson.

 

In the course of their study, the researchers will follow the so-called RRI (responsible research and innovation) guidelines .

 

"We will invite NGOs and others who are interested in seafood production to get input on what social and moral consequences the research and possible implementation could have for Norwegian society. With such input, we can adjust the work underway and create a responsible plan that balances animal welfare, ethics and law," said Robinson.

 

- Nofima