Normalized GAPDH , TUBA and EF1A gene expression. Relative mRNA levels for GAPDH (grey bars), TUBA (dark grey bars) and EF1A (white bars) at times after the addition of either P. salmonis (A) or IPNV (B). Gene expression was normalized by the geometric mean of the three most stable housekeeping genes determined by geNorm in each assay. The 2d and the 6 h controls were used as calibrators (value = 1) in the (A) P. salmonis and in the (B) IPNV assays, respectively. Bars represent the mean values (± SE) for samples from three biological replicates. The asterisk (*) denotes significant differences from calibrators (P < 0.05; Mann-Whitney test).