We have recently investigated the developmental origin of muscle progenitor and stem cells in the zebrafish myotome. Using a combination of lineage analysis, whole somite imaging and gene specific loss of function approaches, we have determined the developmental origin of specific muscle populations during primary and secondary myogenesis in the zebrafish emebryo. We have defined a specific layer of cells functionally equivalent to the amniote dermomyotome, termed the external cell layer which generates distinct muscle populations during embryogeneis. Despite these analyses the cellular basis for the prodigious growth evident in the post embryonic zebrafish myotome have remained undescribed. The work presented here focuses on identifying the source and mechanism of post-embryonic muscle growth in zebrafish. We show that zebrafish possess a compartment of satellite cell-like muscle precursor cells that perjure throughout the post-embryonic development of the fish. Using fluorescent transgene expression and morphometric analysis, we identify the zones of new growth throughout the myotome for larval to adult stages of fish development. Additional fluorescent transgenic lines allow us to investigate the myotomal location and cellular behaviour involved in the transition from an undifferentiated mononuclear MPC into a multinucleate muscle fibre within larval/adult skeletal muscle in vivo. Finally, we use cellular injury and ablation of the mutant and transgenic fish to visualise the role of MPCs in post-embryonic muscle regeneration, and to investigate the genetic programs used.