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Abstract:
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 Lago 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 °C between the surface and 2 m and
0.6 °C 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 dependent 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.
