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The water temperature salmon experience as embryos can shape their future health
Researchers have identified key stages of development when temperature has a major impact on organ formation and long-term health.
Carefully controlled temperatures play a pivotal role in all sorts of production processes.
Take, for example, baking, where delicacies such as macarons, croissants, and soufflés are notoriously difficult to master. They require strict temperature control during baking.
In steel production, controlled heating and cooling cycles determine whether items become strong and flexible or weak and brittle.
In glass manufacturing, small temperature changes can create hidden weaknesses that affect the quality and strength of the final product.
Researchers at the Norwegian University of Life Sciences (NMBU) have now shown that temperature and growth conditions are just as important in nature.
Their research reveals that conditions during the early development of Atlantic salmon embryos can have major consequences for the fish later in life.
Tweaking temperatures
The Salmocode project has major implications for the aquaculture industry, where higher water temperatures are often used during the egg and larval stages to speed up growth.
However, more than 90 million farmed salmon die before reaching slaughter size each year. This raises serious concerns about the ethics and sustainability of fish farming.
Many of these losses are linked to poor organ health, including problems with the heart, kidney, and gills.
Studies have indicated that higher water temperatures in early development can lead to poorer organ development and weaker immune responses in adult salmon.
Until now, limited knowledge of when organs develop has made it difficult to pinpoint the full impact of these farming conditions.
A better and more detailed ‘roadmap’
Early development of Atlantic salmon – from a single fertilised egg into a maturing embryo – is incredibly complex.
Even baking, steel, and glass production look simple in comparison.
To better understand this complexity, the Salmocode project uses an approach called single cell sequencing. This allows researchers to study the developing embryo one cell at a time.
“It gives us a much clearer view of development than traditional methods, which analyse many cells together and can’t distinguish cells that will form different organs,” says project leader Christiaan Henkel.
Using single cell sequencing has enabled the researchers to produce a developmental ‘roadmap’ for Atlantic salmon. It shows how and when different cells and organs form. The roadmap makes it easier to identify how factors such as water temperature affect organ development at different stages.
The most detailed picture yet
The roadmap now covers 30 developmental stages – from fertilised to ‘eyed’ eggs. This is when you start to see the developing embryo’s eyes, which happens prior to egg hatching.
“The roadmap represents data from 140,000 cells across around 50 key cell types; the most detailed picture of early salmon development to date. It will be highly valuable to future research efforts towards improved salmon farming” says Henkel.
The project’s findings also support earlier research on the effects of increased water temperatures.
Salmon eggs raised at natural temperatures (4°C) had low mortality, while eggs exposed to higher temperatures experienced much higher death rates at key developmental stages.
The researcher are now studying the surviving fish to understand how elevated temperatures may disrupt organ development and reduce long-term health and resilience.
Could this influence salmon farming routines?
By looking at more developmental stages and environmental factors like temperature and light exposure, researchers can identify where organ development is most vulnerable.
“Our work could help develop better protocols for egg rearing, preventing developmental problems and ensuring that salmon have a good quality of life, right from the beginning” says Ann-Cecilie Hilling at NCE Aquaculture.
The researchers are working closely with industry, who have been partners in the project and are keen to incorporate project results into their farming practices.
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