Fish larval stage represents a transitional period in which both ontogeny and growth cause substantial changes in structure, physiology, size and morphology. These last twenty years, most of the studies on marine fish larvae development have dealt with the ontogeny and functioning of the digestive tract in order to overcome bottlenecks in larvae culture and weaning processes (switch from live preys to compound diet feeding sequence). These studies clearly demonstrated that fish larvae are not faced to physiological or digestive deficiencies (Zambonino Infante and Cahu, 2001) although they hatch with very immature organs compared to juveniles. More recently, the possible impact of nutritional events occurred during early larvae development stages were considered by different several research groups (Zambonino Infante and Cahu, 2007). Teleosts have similar basic mechanisms of organ development but differences can be found in the relative timing of the ontogeny. For example, the same main morphological and cellular changes occur during the ontogeny of the gastrointestinal tract in Teleost but the timing of the events will be more or less advanced depending on the natural environment temperature (tropical, temperate or cold) of the considered species (Zambonino Infante and Cahu, 2001). Several abiotic and biotic factors, such as water temperature, food availability and composition during early life stages influence the time in organ development and its associated physiological functions. The potential impact of early nutrition on larvae morphogenesis has been probably the most studied these last 5 years, mainly because morphogenesis is the most visible consequence, and therefore the most economically detrimental to aquaculture industry. However, other potential changes, less visible, that could also occurred are more and more considered since they will determine the nutritional and physiological performances of a fish, and therefore its ability to deal with challenges during its subsequent life (Fuiman, 1997). This chapter aims to give an overview of the main developmental events in fish larvae, and describe the impact of early nutrition on the developmental processes that condition the future juvenile potentials.