Prawn larvae of #Macrobrachium amazonicum$ have been collected during six diel cycles in the epilimnion (surface and 2 m) from three different habitats of the Lagos do Rei, Careiro Island. The larval distribution showed a significant increase in density at 22 hours regardless of season or habitat, which suggests a diel vertical migration pattern. The thermal stratification of the lake (mean differential of 0.5° between the surface and 2 m and 0.6° between 2 m and 4 m) suggests that this phenomena could be only partly related to a metabolic efficiency resulting from prawns residing at cooler depths during the day. In shallow tropical waters, predation by visually dependant planktivores can be a more important factor in the adaptative significance of the diel distribution of the macrozooplankton than a low thermal stratification. The diurnal feeding activity found in the predominant planktivores fish species of the Careiro lake reinforces this hypothesis. (Résumé d'auteur
