Epigenetics We characterized DNA methylation response to winter, smoltification, and seawater by RRBS from liver at four key time points: before winter (week 1) immediately after winter, but before smoltification (week10) immediately before seawater transfer, but after smoltification (week 19) and after seawater transfer (week 25). Fish were split into replicate control tanks after the first sampling (week 1) and again before seawater transfer (week 25). Sampling began 21 weeks after first feeding (first feeding, 5 weeks after hatching). Immediately after the week 19 sampling, 20 fish from each tank were transferred to seawater conditions at the Norwegian Institute for Water Research (NIVA), Solbergstranda, Norway. UV-sterilized seawater used in this life-stage had a salinity of 3%-3.5% and was obtained from the Oslofjord. samples of liver were cut into ~5mm cubes and placed in RNAlater. Samples were incubated for at least 30 minutes at room temperature before long-term storage at -20°C. The samples were processed with Ovation RRBS Methyl-Seq System and bisulfite treatment was done with the Epitect Fast Bisulfite Conversion kit. RRBS libraries were controlled with a BioAnalyser machine on DNA1000 chips. Paired-end sequencing was performed by Novogene with a HiSeq X sequencing machine from Illumina