Craig Primmer – The mysteries of salmon puberty

The salmon of the Baltic reach maturity younger and younger. Because of this they return to their home rivers smaller than before. The reason is still unclear but the gene VGLL3 may be the key to solving this mystery, and may explain questions of human puberty as well.

Hundred thousand salmon eggs. This is the cargo that Craig Primmer, professor of genetics, intends to bring with him to the Viikki Campus this autumn.

And it’s not just any old roe, the eggs will be specifically bred for his research from stocks of Baltic salmon. The gene VGLL3 plays a crucial role. In 2015, Primmer and his Norwegian colleagues proved that it regulates the age at which a salmon reaches sexual maturity.

 “VGLL3 is a regulating gene, which tells other genes to switch on and off. By creating several stocks with different versions of VGLL3 in a controlled environment, we will be able to monitor how great the gene’s significance really is,” Primmer explains.

At the beginning of 2018, the salmon will be moved to the Lammi Biological Station into facilities specifically built for them. The intention is to study them in tanks where the food and water temperature can be controlled. This stage will take from two to three years.

Studying salmon puberty is interesting, because it has such a clear impact on the lifespan of the salmon.

Salmon migrate from their home rivers to live in the ocean from one to five years, until puberty brings them back to the rivers.

The ideal age of sexual maturation is lower for male salmon than it is for females. It’s enough for a male to have the strength to swim up the river to mate, but a female must also be able to build a nest out of pebbles (called a ‘redd’) for the eggs to protect them from the current.

During the past few years, salmon have, on average, started to reach puberty earlier. The reason for this is unknown, but Primmer’s research may shed some light on the issue.

Why spend years and millions of euros to determine the age of puberty in salmon?

 “First and foremost, this is fundamental research. I’m a geneticist, so I am primarily interested in how genes cause changes in free-living populations. Salmon are a very interesting case in this sense, as there are a number of of populations that differ slightly from one another,” says Primmer.

The research also has applied benefits. Salmon reared for aquaculture typically reach puberty early and do not grow as large as the producers hope. Our research can help determine why this happens.

And as is often the case with fundamental research, this work can also yield unexpected applications. In 2014, it was established that the same VGLL3 gene is also linked with puberty in humans. Last year, a study indicated that VGLL3 may play a central role in certain gender-specific immunological diseases.

Primmer was surprised.


Craig Primmer

Professor Primmer held his inaugural lecture An Evolutionary Genomics Fish Tale on Wednesday 29 November 2017.

University of Helsinki new professors

Recording of the lecture