Teleost fish are more diverse than any other vertebrate group, and yet only a limited number of species are fished and farmed globally. Efforts to expand the quantity and diversity of fish produced are hampered by the extreme diversity of ontogenetic responses of fish, especially during larval development. This review looks at advances in molecular phylogeny, endocrine and nutrient influences and long-term studies of the phenotypes of commercially important fish to put the sources and consequences of this plasticity into context. This nested context of evolutionary forces of the fish-specific genome duplication, epigenetic influences, ontogenetically conserved processes like metamorphosis and cell determination is further presented in relation to how fish larvae translate the environment into somatic signals, the teleostian diversity of internal processes like sex differentiation and somatogenesis, and the long-term practical consequences of changes in timing or anthropogenic influences. This review aims to present a new baseline of knowledge of marine fish larvae which is useful to scientists, managers and producers.