Abundance and body size variations of the prawn #Macrobranchium amazonicum$ (Heller, 1862) have been studied in a Central Amazonian floodplain lake, on Careiro Island. The highest number of captures and smallest sizes have been observed beneath floating macrophyte meadows. This suggests that these meadows serve a nursery habitats. The densities registered in the Amazon river were three times lower than in the lake. Maximum densities were recorded during low water periods, while minimum densities were found during high water periods. These results point to a relationship between current force and catchability. In the floodplain lake, prawn abundance seems to be related to macrophyte expansion during the periods of rising water, the lowest captures were registered at high water, which is probably due to the spatial dispersion as the water volume increases. River prawn populations are characterised by larger sizes than the ones in the lake. (D'après résumé d'auteur
