Celeste Jacq helped find the maturation gene using DNA and growth patterns in fish scales from 1,500 salmon. Photo: Jon-Are Berg-Jacobsen/Nofima

Project Year 2016

Salmon puberty gene discovered

Nofima scientists have helped identify the salmon maturation gene – a major international breakthrough with major potential for farming.

The gene explains 39% of the variation for when salmon reach sexual maturation. This is uncommon, as sexual maturation is thought to usually be controlled by a large number of genes. The team found that in a specific area of the gene, there are two variants that determine whether a salmon returns to the river to spawn as a small or large fish. Salmon that have two copies of the “small” gene variant will almost certainly become sexually mature while still relatively small. Salmon with two copies of the “large” gene will almost certainly not reach maturation until they have grown larger. The right combination “However, what is unique about this discovery is that for salmon that have one of each variant, gender determines when the fish will mature, and thus how big it will be. There is very little prior research showing that gender plays a role in how a gene is expressed,” says Nofima scientist Celeste Jacq, one of the authors of the article published in Nature. This research will be very useful in the management of wild salmon stocks and for breeding companies. “Breeding companies can control the prevalence of these gene variants in their broodstock, since the markers of the maturation gene make it possible to select the desired variant. This knowledge is freely available through the publication in Nature,” says Jacq. Premature sexual maturation Until now, breeding companies have only known when a fish will reach sexual maturity after it has occurred. Now, with the marker for this gene, salmon with early sexual maturation can be identified by genetic testing at the fry stage and be removed from the population. In this way, fish that are going to mature early will not be reared as potential broodstock. Some breeding companies have already begun removing suspected early maturing fish based on this finding, to prevent the fish they set out to sea reaching sexual maturity prematurely

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