In French Guyana, the dynamics of young prawn migrations from marine to estuarine waters remains equivocal, raising the question of habitat utilization in the adjacent mangrove systems. The temporal distribution of juvenile penaeid species was thus investigated in the main drainage channel of a Guianese coastal mangrove. A total of 2275 juvenile prawns belonging to five species, including two penaeid species (Penaeus subtilis, Xiphopenaeus kroyeri) were collected by stake net on four occasions during the wet season. Catches were dominated by large-sized, highly-valued P. subtilis and exclusively occurred (a) at the end of flood tide and (b) at the beginning of ebb tide, when water velocity was maximum. Size structures were very similar between flood- and ebb tides, suggesting that the same assemblages entered then withdrawed from the mangrove on a given tidal cycle. Residence times of prawns in the mangrove were short (3-4 hours per tidal cycle), as juveniles gained access to the coastal mangrove only a few hours per day during high tide. These results will need further confirmation at larger (Guianese) scale, but provide evidence for original, tidal-dominated mangrove utilization patterns by juvenile prawns. Given the economic importance of P. subtilis in French Guyana, there is an urgent need to assess the contribution of coastal mangrove habitats to sustaining near shore fisheries.