The intertidal mangrove forest habitats, open water channels and adjacent marine areas are considered important spawning grounds and nursery areas for estuarine and marine fishes. The present study investigated the fish species assemblages, found in the intertidal mangrove forest during high and low tides, and describes the ecological strategies of the intertidal fish assemblage to minimise predation and desiccation in the mangrove forest during low tide. Moreover, this study describes the seasonal changes of the fish species composition in relation to biomass, density and species number in the tidal creeks of Furo do Meio and in three areas (upper-, middle- and lower estuary) of Caeté River main channel. Fish were collected at regular intervals from mangrove tidal creeks and Caeté River main channel. In the intertidal mangrove forest the samples were taken at the end of each season (December/96 and July/97). In addition, samples were taken to evaluate the moon influence on the fish species composition in the upper estuary during each yearly astronomical tide (September/96 and March/97). The fish fauna of each habitat was different in density, biomass and species composition. Mean density and biomass were estimated for the mangrove forest during low tide (2.8 ind m-2; 17.4 g m-2), the mangrove tidal creeks of Furo do Meio (0.11 ind m-2; 2.1 g m-2) and the Caeté River channel (0.2 ind m-2; 0.9 g m-2). Analysis of the catch data showed that in the mangrove forest the total number of species and total biomass during low tide were significantly different in time and space. For the most important species captured in the mangrove forest during low tide (Myrophis punctatus, Poecilia sp. and Gobionellus smaragdus) densities and biomass differed significantly among species. For the creeks of Furo do Meio the analysis of the catch data showed that the number of species varied significantly between creeks and the total fish biomass differed significantly between seasons. In the Furo do Meio, densities and biomass were significantly different between seasons for Cathorops pleurops and Colomesus psittacus. In the Caeté Estuary the number of species, total density and total biomass differed significantly amongst areas and seasons. For the most important species captured in Caeté Estuary (Cathorops spixii, Aspredinichthys filamentosus, Aspredo sp2, Pimelodus blochii, Pseudauchnipterus nodosus, and Macrodon ancylodon) except those of Stellifer rastrifer, Stellifer microps, Aspredo aspredo, Aspredo sp1 and Cynoscion acoupa, the mean density differed significantly amongst seasons. Furthermore, the analysis of catch data showed that the mean biomass of these species, with exception of S. microps and Aspredo sp1, differed significantly amongst season. The moon phase analysis of the catch data showed that all variables (number of species, total density, total biomass and for densities and biomass of the most important species), except for A. aspredo (density and biomass) were significantly different between moon phases. In addition, moon phase x month interactions were significantly different (p<0.01) for all variables, except for S. rastrifer (density) and A. aspredo (biomass). In other words, the lunar influence on the fish distribution in the upper estuary varies according to the month (season). In the Caeté Estuary the fish species are distributed in two main habitats (main channel of Caeté River and intertidal mangrove forest). Both habitats showed a very different fish species composition and the fish species in each habitat have different strategies to overcome the seasonal and tidal instability. Seasonal salinity fluctuation is the main factor, which structures the fish assemblage in the estuary. The number of species recorded, the density and biomass in the various habitats of Caeté Estuary were compared with published data from other tropical and subtropical estuaries in the world. In this study, the different levels of estuarine dependence for the most important species captured in the Caeté Estuary were discussed. In conclusion, at least 85% of the species captured by the artisanal and subsistence fisheries in the Bragantine region require estuarine conditions to complete their life-cycle.