Abstract

Fish represent more than half of the vertebrate species in the world. In the Tocantins River, the second largest river by water flow in Brazil, there are a minimum of 520 species of fish. This work aims to list the diversity of the ichthyofauna present in the Cacau River, a tributary of the Tocantins River, which flows into the municipality of Imperatriz, Maranhão. The collections took place over a period of one year, every first week of the month, both in the rainy season (November to April) and in the dry season (May to October). The specimens were captured using cast nets and gillnets with meshes of 8, 10, 12, and 14 cm between opposite nodes, which were submerged for approximately 4 h a day. Greater species diversity was demonstrated in the dry period, from April to October. The Neotropical ichthyofauna database consisted of a total of 263 individuals from the Cacau River. The occurrence of 31 species was recorded, distributed in among 25 genera, 15 families, and 4 orders were recorded.