Stem cell surrogacy offers new way to preserve threatened salmon genetics.
Sterile farmed salmon fitted with stem cells from wild donors have produced thousands of offspring carrying wild salmon genes in a Norwegian research project that could open a new tool for conservation and breeding.
Researchers at Norway’s Institute of Marine Research (HI) have, for the first time in Atlantic salmon, used so-called surrogate broodstock technology to generate progeny from wild salmon donors by transplanting their germ cells into sterile farmed fish.
“This is a form of surrogacy,” researcher Lene Kleppe said. “We take germline stem cells from selected individuals and transfer them to other individuals, that is, to surrogates, which can then produce offspring.”
The surrogate fish used in the trials are triploid salmon that have been made sterile through pressure treatment of the egg. They do not produce functional eggs or sperm on their own and would not have any offspring without the transplanted donor cells, Kleppe noted.
Under the method, germline stem cells are harvested from a donor fish at an early developmental stage. These cells can later develop into either eggs or sperm, depending on the sex of the surrogate that receives them. Cells are injected into juvenile fish before the immune system is fully developed, which prevents rejection and allows the donor cells to integrate into the host.
In the HI experiment, cells from a single donor were injected into both female and male surrogates, where they later developed into eggs in females and sperm in males.
Because germ cells from just a few donors can be transplanted into multiple surrogates, the approach can multiply the amount of genetic material from rare individuals and could be used to support small or threatened salmon populations, provided genetic diversity is carefully managed.
“In a reduced stock, the genetic material can be limited, which makes it challenging to ensure that future generations have enough genetic variation,” Kleppe said. Reduced variation makes a population less able to adapt to change and survive over time.
A key advantage of the technology is the potential to build long-term “gene banks”. Germline stem cells from threatened species or stocks can be frozen and stored for years. While sperm has long been cryopreserved, eggs do not tolerate freezing in the same way. By banking stem cells that can become either eggs or sperm, researchers can preserve genetic material from both females and males even when wild populations are in poor condition.
If a population collapses, closely related species can in some cases act as surrogates. In Japan, for example, a small mackerel species has been used as a surrogate to produce sperm for the much larger Pacific bluefin tuna, according to Kleppe.
Surrogate broodstock technology was originally developed in Japan and has been tested on several species internationally. The new Norwegian work, described in Aquaculture under the title “Production of donor-derived Atlantic salmon progeny using allogeneic surrogate broodstock technology”, represents the first demonstration in Atlantic salmon in Norway.
The method remains at the experimental stage for Atlantic salmon. HI has several ongoing projects and has recently secured additional funding from the Research Council of Norway to optimise efficiency and assess how the technology could be applied in practice, both for conservation of wild stocks and for preserving the genetics of high-performing farmed lines.
“So far we have shown that this method can be used with salmon as both donor and surrogate,” Kleppe said. “There is still some way to go before it can be used efficiently in practice, which is what we will look at in the new project.”
