Acclimation: differential expression at each time period of heat stress versus fish held at control temperatures across all strains. Results for a) Day 1 of heat stress treatment; b) Day 3 of heat stress treatment; c) Day 7 of heat stress treatment; and d) Day 28 of heat stress treatment. The number of significant genes was 7,833 at Day 1 (4,058 upregulated, 3,775 downregulated), 6,408 at Day 3 (3,344 upregulated, 3,064 downregulated; 18.2% decrease from Day 1), 3,624 at Day 7 (1,958 upregulated, 1,666 downregulated; 53.7% decrease from Day 1), and 1,269 at Day 28 (719 upregulated, 550 downregulated; 83.8% decrease from Day 1). Genes that are significantly differentiated (FDR ≤ 0.05) are in red and those that are not significant are in black. On a log2 scale, the green lines show genes that are ≥ 2 fold, and the blue lines designate genes that are ≥ 4 fold. The x-axis is the mean expression of each gene in counts per million reads (CPM) on a log2 scale.