Swim training of adult zebrafish promotes hyptrophy and vascularization of fast skeletal muscle fibers through activation of myogenic and angiogenic transcriptional programs

In zebrafish, as in other teleost species, swimming-induced contractile activity under sustained conditions potentiates somatic growth. In the present study, we aimed at investigating the cellular and molecular adaptative mechanisms that take place in the fast skeletal muscle of adult zebrafish in response to swimming. By performing microarray analysis we have identified over four thousand significantly differentially expressed genes in skeletal muscle that are involved in different processes such as muscle growth and development, muscle contraction, angiogenesis, metabolism and immune-related genes. Moreover, swim training increased fibre size (i.e. hypertrophy) and vascularization in fast muscle. These results show that exercise produces meaningful changes in the fast muscle transcriptome and suggest that fibre hypertrophy may be responsible for the growth-promoting effects of exercise accompained by a switch to a more oxidative capacity of white muscle fibres to fuel the energy demands imposed by swimming. These findings provide insight into the cellular and molecular adaptive mechanisms underlying the swimming-induced potentiation of growth.