Abstract
In Atlantic salmon aquaculture, early sexual maturation represents a major problem for producers. This is especially true for grilse, which mature after one sea winter before reaching a desirable harvest weight, rather than after two sea winters. Salmon maturing as grilse have a much lower market value than later maturing individuals. For this reason, most companies desire fish that grow fast and mature late. Marker-assisted selection has the potential to improve the efficiency of selection against early maturation and for late sexual maturation; however, studies identifying age of sexual maturation-related genetic markers are lacking for Atlantic salmon. Therefore, we used a 6.5K single-nucleotide polymorphism (SNP) array to genotype five families from the Mainstream Canada broodstock program and search for SNPs associated with early (grilsing) or late sexual maturation. There were 529 SNP loci that were variable across all five families, and this was the set that was used for quantitative trait loci (QTL) analysis. GridQTL identified two chromosomes, Ssa10 and Ssa21, containing QTL related to grilsing. In contrast, only one QTL, on Ssa18, was found linked to late maturation in Atlantic salmon. Our previous work on these five families did not identify genome-wide significant growth-related QTL on Ssa10, Ssa21, or Ssa18. Therefore, taken together, these results suggest that both grilsing and late sexual maturation are controlled independently of one another and also from growth-related traits. The identification of genomic regions associated with grilsing or late sexual maturation provide an opportunity to incorporate this information into selective breeding programs that will enhance Atlantic salmon farming.
Highlights
The Atlantic salmon (Salmo salar) exhibits a great deal of variability in age and size at sexual maturation
Families were part of a commercial broodstock program developed by Mainstream Canada and based on the Mowi strain of Atlantic salmon, which was derived from a breeding program established using Norwegian populations (Gjedrem et al 1991)
Previous studies performed in rainbow trout and Arctic charr have shown an apparent link between quantitative trait loci (QTL) for sexual maturation and growth (Haidle et al 2008; Martyniuk et al 2003; Moghadam et al 2007); our results indicate a different scenario for Atlantic salmon in the Mainstream Canada breeding program
Summary
The Atlantic salmon (Salmo salar) exhibits a great deal of variability in age and size at sexual maturation. The timing of sexual maturation is controlled by a complex process that involves genetic and environmental components (Thorpe and Metcalfe 1998) Internal factors, such as age and lipid reserves, together with external factors, like light abundance, temperature, and food intake, seem to have an impact on the initiation of sexual maturation (Gardner 1976; Herbinger and Friars 1992; Simpson 1992). There is a genetic component to age at sexual maturation in Atlantic salmon, and estimates of heritabilities (h2) for this trait in Atlantic salmon range widely from 0.09–0.17 (Gjerde et al 1994; Wild et al 1994; Gjedrem 2000) to 0.39 (Gjerde and Gjedrem 1984) to 0.48 (Gjerde 1984) These observations strongly indicate that age at sexual maturity in Atlantic salmon is a heritable trait. It should be possible to select for Atlantic salmon that do not become sexually mature as grilse and for late sexually maturing fish
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