Following a selection program carried out for five generations in our lab, we examined the impact of selection on the growth regulation pathways occurring in the brain, hypophysis, liver, and muscle in brook charr. Thirteen families from the selection program and 16 control families were sampled at age 1+. The four best and the four worst performing families were sampled in each line. The gene expression levels of three reference and 10 candidate genes were analyzed by real-time PCR. Family performance and individual size were shown to have no impact on gene expression levels. However, selection was itself the key factor for differential expression. The gh/igf-1 axis in the selected line was upregulated, including pituitary igf-1r, liver ghr and igf-1, and white muscle ghr and igf-1r; this resulted in better growth performance (weight and length). However, improved growth performance did not seem to be related to the differential expression of genes involved in appetite control (npy, lepr, grl, srifr) or muscle construction (mhc, myog). This study highlights how transcriptomics may be useful for understanding the roles of different key endocrine steps regulating physiological performance. Large variations still exist in the selected line, indicating that the full genetic selection potential has not yet been reached.