Field trial of CRISPR sterile salmon delayed until spring

A field trial of the sterile offspring of gene-edited salmon that was due to take place in a Norwegian fjord has been delayed until at spring at the earliest.

The Institute of Marine Research (IMR) planned to stock 303 sterile salmon, along with 485 non-sterile fish from the same family, in four small pens contained within a larger pen at its Matre research station.

But the Norwegian Scientific Committee for Food and Environment (VKM), which carries out independent risk assessments for the Norwegian Food Safety Authority (Mattilsynet) and the Environment Agency, assessed the field trial as too risky.

VKM says there is a low probability that some of the apparently sterile fish might be fertile, and that in a “worst case scenario” would manage to escape and spread the sterility genes to wild fish by introgression.

'Lack of expertise'

IMR argues that much of what VKM concludes is based on misunderstandings and a lack of expertise but has agreed to provide further information and carry out an extra round of genotyping on the fish they want to stock to reassure authorities.

This work, and the time it will take for the Norwegian Environment Agency to process the information, means the trial won’t take place until the spring of 2024 at the earliest. In the meantime, the fish will remain in tanks on land.

Anna Wargelius, head of research at the IMR’s Department of Reproduction and Developmental Biology, and leader of the experiment, told Fish Farming Expert’s Norwegian sister site, Kyst.no, that researchers were now working on compiling extra data.

“Since there were several misunderstandings in the previous round, we plan to spend a little more time making the supplementary data clear and distinct. Therefore, I think it is likely that it will take until Christmas or mid-January before we are ready with all supplementary data in the case,” said Wargelius.

“This will also be good before the salmon possibly go into the sea, as it is better to postpone the release until spring and a little warmer in the sea, so that we avoid problems with welfare associated with winter temperatures in the sea experiment.”

Alternative to triploidy

The project by the IMR is part of ongoing research into using gene editing as an alternative way of producing sterile farmed salmon so that they are unable to mate with wild Atlantic salmon if they escape. Sterility also prevents problems associated with early maturation.

Atlantic salmon can be rendered sterile by pressure or temperature treatment of newly fertilised eggs to produce triploids, which are functionally sterile due to having a third, unpaired set of chromosomes. But triploids often perform poorly on commercial fish farms and the production of triploid salmon in Norway has been put on hold due to welfare issues of the fish.

Scientists at IMR have previously used the CRISPR gene editing technique to create sterile salmon – trademarked VIRGIN salmon - by preventing the formation of germ cells that develop into gametes (reproductive cells). The technique involves microinjecting a CRISPR-Cas9 “construct” at the egg stage.

By adding a protein to the egg at the same time as the CRISPR construct, they were then able to create a genetically sterile broodstock fish with germ cells – called “VIRGIN rescued salmon” - which in turn can produce sterile offspring for production. It is these offspring which will be used in the field trial.

NOK 1bn in savings

The VIRGIN salmon was developed with the help of a NOK 7.9 million award from the Research Council of Norway, which says the fish could solve some major challenges in salmon farming.

“Farming companies are demanding improved methods for production of sterile salmon and are potential customers. Licensing or sales of IPR (intellectual property rights) are realistic business models. The Norwegian salmon farming industry may have annual savings for more than 1 billion NOK,” the Council said.

Read more about VIRGIN salmon here.