ABSTRACT The present work aims to characterize a fish assemblage from a northeastern Brazilian estuary according to its diet and trophic organization along the estuarine-reef gradient. Sampling was performed at the Mamanguape Estuary, and fishes were collected using three types of nets at seventeen sites, grouped into four regions according to salinity range: reefs and the lower, middle, and upper estuary. The most abundant species were Atherinella brasiliensis, Mugil curema, and Sphoeroides testudineus. The highest species abundance and richness was observed for the lower estuary. Zooplankton was the most consumed category, recorded for forty-two species. Among the guilds, piscivores were the most abundant, followed by crab eaters. Herbivores, mostly represented by Abudefduf saxatilis, had a higher abundance in reefs, being correlated according to ANOSIM analysis to this region, while piscivores and crab eaters showed a high contribution to inner regions of the Mamanguape Estuary.