In an experimental laboratory study with a population originating from the mouth of the Amazon River, Brazil, we tested the early larval stages of the prawn Macrobrachium amazonicum for their dependence on planktonic food sources. As criteria for an uptake and conversion of food (Artemia nauplii), we measured changes in larval dry mass and elemental composition (carbon, hydrogen, nitrogen), as well as rates of survival and development. Experiments conducted with larvae from three different females showed consistently that the first zoea is a non-feeding stage (obligatory lecithotrophy). While survival and duration of development through the Zoea II stage were still not affected by absence or presence of food, fed larvae showed significant growth (indicating facultative lecithotrophy). The third zoeal stage exhibited still a high level of independence from food, surviving for extended periods (up to another 11 days, or 15 days from hatching) in complete absence of food. In contrast to the Zoea II, however, this stage was under conditions of continued starvation no longer capable to moult the subsequent stage IV (obligatory planktotrophy). In summary, the ontogeny of larval feeding consists in M. amazonicum of gradual changes from complete food-independence (Zoea I), through facultative lecithotrophy (Zoea II), to obligatory planktotrophy (Zoea III and all later stages). Reduced nutritional vulnerability in the early larval stages, together with an initial tolerance of freshwater, allows for hatching in oligotrophic riverine environments and survival during the period of subsequent larval downstream transport towards estuarine waters, where both average salinity and plankton productivity are higher.