LARVANET is a COST Action including researchers and producers working with fish larvae. The Action intends to integrate knowledge obtained in national and European research projects, as well as practical experience, in order to improve quality of fish larvae used in aquaculture. The subject of this literature review is fish ontogeny and its impact on larval and juvenile viability and quality. It focuses on fundamental biological knowledge relevant to larval phenotype and quality and in particular, on the development of white muscle and factors that may affect it. It also discusses the available methodologies to assess growth and larvae/juvenile quality, and identifies gaps in knowledge and further research directions.