Seasonal and genetic effects on lipid profiles of juvenile Atlantic salmon

Seasonality can influence many physiological traits requiring optimal energetic capacity for life-history stage transitions. In Atlantic salmon, high-energy status is essential for the initiation of maturation. Earlier studies have linked a genomic region encoding vgll3 to maturation age, potentially mediated via body condition. Vgll3 has also been shown to act as an inhibitor of adipogenesis in mice. Here we investigate the influence of season and vgll3 genotypes associating with early (EE) and late (LL) maturation on lipid profiles in the muscle and liver of juvenile Atlantic salmon. We reared Atlantic salmon for two years from fertilization and sampled muscle and liver during the spring and autumn of the second year (at which time some males were sexually mature). We found no seasonal or genotype effect in the muscle lipid profiles of immature males or females. However, in the liver we detected a triacylglycerol enrichment and a genotype specific direction of change in membrane lipids, phosphatidylcholine and phosphatidylethanolamine, from spring to autumn. Specifically, from spring to autumn membrane lipid concentrations increased in vgll3*EE individuals but decreased in vgll3*LL individuals. This could be explained by 1) a seasonally more stable capacity of endoplasmic reticulum (ER) functions in vgll3*EE *EE individuals compared to vgll3*LL *LL individuals or 2) vgll3*LL *LL individuals storing larger lipid droplets from spring to autumn in the liver compared to vgll3*EE *EE individuals at the expense of ER capacity. This genotype specific seasonal direction of change in membrane lipid concentrations provides more indirect evidence of a potential mechanism linking vgll3 with lipid metabolism and storage.