Differential expression analysis and a transcriptome assembly were conducted using 101 bp PE reads from Illumina HiSeq 2000. Samples from the liver of male Arctic char (Salvelinus alpinus) were collected after one month temperature acclimation at 8 °C or 15 °C in July at three time points: middle of dark period at 01:30 (tp1), middle of light period at 12:30 (tp2) and one hour before dark period at 20:30 (tp3). The de novo assembly was constructed using a total of 170 M reads from two males using Trinity v.2, reads aligned using Bowtie2 and read counts obtained using Corset. Only transcripts from genes with at least 1 cpm in at least three samples were included in the assembly.