Sterile salmon: the parents determine whether the fish is healthy or not

Triploid salmon are farmed fish made sterile by subjecting fertilized eggs to pressure treatment.

– The eggs are exposed to high pressure shortly after fertilization, which results in the fish retaining three sets of chromosomes instead of the usual two. This makes the salmon triploid and sterile, explains researcher Aurélien Delaval.

The benefit of sterile salmon is that they cannot breed with wild salmon, reducing the risk of genetic mixing and preserving wild populations.

But triploid salmon also come with challenges.

– If the pressure treatment is lower than optimal, it can lead to chromosome inheritance problems, says Delaval, adding:

– We suspected that this might be the reason why triploid salmon tend to have poorer health and slower growth than other farmed fish. But it turns out the fish’s family background matters even more.

Health challenges in sterile salmon

Triploid salmon are generally less healthy than normal diploid salmon.

– Triploids are more prone to skeletal and heart deformities, cataracts, infectious diseases, and skin ulcers, says Delaval.

Read more about the challenges and opportunities with triploid salmon.  

The researchers thought at first that the poorer health and growth in triploid salmon might be due to the eggs not receiving enough pressure to successfully induce triploidy.

They decided to put that hypothesis to the test.

What happens when the pressure is not optimal?

The researchers exposed salmon eggs from different families to five pressure treatments:

• One with no pressure (0 PSI), producing regular diploid fish
• One with full pressure (9500 PSI), the standard to induce triploidy
• And three intermediate treatments with lower, suboptimal pressures (ranging from 6500 to 8500 PSI)This allowed them to compare how the offspring from various family groups developed following different pressure treatments.

– Our results showed that suboptimal-pressure treatments caused genetic issues in many of the eggs, and many of them didn’t hatch at all, says Delaval.

Among the few fish that did survive the suboptimal-pressure treatments, there was a mix of regular diploids, where the pressure had no effect, and true triploids where the treatment worked as intended.

– This let us investigate whether suboptimal pressure alone affected the subsequent health and growth of the fish—or whether the fish’s family background was more important, says Delaval.

Clear differences among triploid families

The findings showed that a fish’s family lineage had a greater impact on health and growth than the pressure treatment itself.

– Some triploid families performed better than others, with some performing similarly to their diploid siblings Delaval explains.

– For example, triploid fish from certain families had few or no skeletal deformities, while others showed more frequent and severe deformities. We also saw clear differences in growth rates and mortality among triploid families.

This suggests that selective breeding could be an important tool in improving the welfare of triploid salmon.

– Our next step is to study this more closely, so we can better understand how selective breeding might help improve welfare and performance in triploid salmon, says Delaval.

About the project

The TripGenWelfare project is funded by the Research Council of Norway. Its aim is to explore the genetic causes of welfare and performance challenges in triploid salmon, including whether the pressure treatment plays a role.

Reference

Delaval, A., Glover, K. A., Solberg, M. F., Fjelldal, P. G., Hansen, T. J., Pedersen, A. Ø., Sambraus, F., Garnes-Gutvik, S. N., & Harvey, A. C. (2025). Inducing failed triploidy: The effects of sub-optimal hydrostatic pressure treatments on Atlantic salmon growth and welfare. Aquaculture, 608, 742743.