Due to the importance of fish in human food and ecosystem maintenance, the aim of this study was to identify, characterize and classify according to the scientific nomenclature and its external morphology, the species of captured fish in the fields of São Bento, located in the Baixada Maranhense microregion. All species of fish collected were fixed in 10% formaldehyde. In this study, 11 families were identified, of which: Astyanax bimaculatus, Colossoma macropomus, Metynnis lippincottianus, Pygocentrus nattareri and Charax gibbosus belonging to Characidae family; Steindachnerina bimaculata belonging to Curimatidae family; Hoplerythrinus unitaeniatus and Hoplias malabaricus belonging to Erythrinidae family; Prochilodus lacustre belonging to Prochilodontidae family; Megalops atlanticus belongs to Megalopidae family; Gymnotus carap belonging to Gymnotidae; Crenicichla mezesi, Heros severus and Tilápia rendali belonging to Cichlidae family; Trachelyopterus galeatus belonging to Auchenipteridae family; Megalechis thoracata belongs to Calillichthyidae family; Pimelodella cristata belonging to Heptapteridae family; Hypostomus plecostomus and Loricaria cataphractae belonging to Loricaridae family; and, finally, Synbranchus marmoratus and S. sp belonging to Synbranchidae family. In the fields of São Bento was found a wide variety of species of fishes, and, from 21 species, Prochilodus lacustre, Hypostomus plecostomus, Loricaria cataphractae, Colossoma macropomus and Tilápia rendali are not native to this region.