We suggest that training-induced cardiac enlargement involved a mixture of hyperplasia and hypertrophy, given the higher protein levels of PCNA and the higher transcript amounts of the morphogenic- and hypertrophic-related genes MEF2C, GATA4 and ACTA1. Cardiac growth in salmonids can also occur via both above-mentioned mechanisms in response to anemia or sexual maturation [19]–[21]. This evidence concerns the gene GATA4 and anemia.