Monthly sampling from march 1981 to april 1983 using beach seines, cast nets and gill nets indicated six species, Xenomelaniris brasiliensis, Brevoortia pectinata, Geophagus brasiliensis, Gerres aprion, Genidens genidens and Achirus lineatus, as the most abundant fishes in the Marependi Lagoon, Rio de Janeiro, BraziL The species presented a long reproductive period and the recruitment distributed throughout the year. Analysis of the mean catch per unit effort in relation to month, sampling areas, and environmental factors along with analysis of the length frequency distribution by depth strata indicated that the spatial distribution, related to depth and occurrence of submerged aquatic vegetation seem to be the main factors regulating the species distribution. Alteration of the environmental conditions in the lagoon due to the opening of the Marapendi channel in 1984 caused significative modification in the distribution and abundance patterns of the main species. The impact of these alterations in the Marapendi Lagoon fish community has yet to be determined.