SALMAT: Climate change will increase early maturation in salmon aquaculture which can be mitigated via genes controlling puberty

The time of maturation gene of salmon has been identified in this project. Probably it is a related mechanism that initiates puberty in humans. The discovery can now be used to breed salmon that matures late. It provides better welfare for farmed fish. To find the genetics that determines the time for sex maturation of salmon, the entire genome of salmon maturing either early or late were sequenced. The salmon came from six rivers in western Norway. The methodology identified a region in chromosome 25 that helps determine the age at maturity in salmon. This region is also previously linked to the time of puberty in humans. The finding supports the theory that there may be a general mechanism for controlling the age of maturation in vertebrates. In salmon aquaculture, early maturation is negative. Early maturing salmon display reduced growth, weakened resistance to disease and poorer meat quality. The ideal is that the salmon is still immature at slaughter. Our results show that early maturation rate is reduced if we use stocks of salmon maturation having the late maturation alleles. In addition, the risk of genetic impact from escaped salmon may be reduced since late maturing fish have a higher likelihood of dying before they can spawn. In addition to the fact that late maturation provides better welfare for farmed fish and thus contributes to more sustainable salmon production, the genetic predisposition of time of maturation can be used in the management of wild salmon. The governmental authorities can tell thereby tell how many early maturing and late maturing fish there are in wild stocks of salmon. By looking at this for several years, one can see how the reproductive strain changes in salmon, which may produce better knowledge for how to take care of the wild salmon strains. We have also seen that the time of maturity gene is regulated in the testicle of male animals when they enter puberty. We believe that the gene is associated with the proliferation of the somatic cells in the gonad. Our studies have contributed to increased knowledge of puberty in vertebrae, since it is possible to explain how the puberty is molecularly induced if you know the function of the proteins encoded by the genes in question. This knowledge can contribute to basic understanding of puberty in vertebrates.

State-of-the-art genomic and bioinformatics methods, in combination with a unique collection of biological samples from both wild populations and multiple-generation experiments already conducted, will be implemented to address the projects primary goals. The first approach will be to conduct massive parallel resequencing of entire genomes from wild salmon individuals and strains displaying different age at puberty (early, intermediate and late). Such subsamples will be studied in the South and the North of Norway. This will aid finding regions under selection for time of puberty. The second approach will be to use a material bred for the dwarf male phenotype over two generations. Genome resequencing and SNP chips will reveal regions under selection in th is material. The third approach is based on compiling orthologous genes involved in reproduction and growth in the salmon genome. Data obtained from genome resequencing of wild strains, SNP analysis of dwarf males and candidate genes will be mapped to the salmon genome. Bioinformatic analysis will reveal regions under selection. Since the age at puberty is strongly modulated by environmental factors such as light and temperature, epigenetic programming of puberty will also be investigated. In order to ide ntify the molecular mechanisms of such modulation we will use clonal lines subjected to different light and temperature conditions to characterize the effects epigenetic programming of maturation.