T direction of fold change. Primers were designed to ensure equal amplification for all species to ensure correct estimates of expression levels, as shown for collagenase-3 log2(qPCR) against log2 (microarray) shown for (B) Atlantic and (C) pink salmon. chm = chum; pnk = pink; atl = Atlantic; AK = anterior kidney; S = skin; gene acronyms are as per the primer table (Additional file 4: Table S2). A