Reproductive cycle of the flying fish Hemiodus unimaculatus (Bloch, 1794) (Characiforms: Hemiodontidae) in the upstream area of the Tucurui hydroelectric plant, Pará, Brazil

The reproductive cycle of Hemiodus unimaculatus in the upstream area of the Tucuruí reservoir in the Tocantins River was described. The animals were collected monthly for 1 year in the Tauiry Village, municipality of Itupiranga, Pará. The individuals had their biometry taken, the gonads removed and weighed to calculate the gonadossomatic index and processed for histological analysis. A total of 103 animals were collected, 87 females and 16 males (sex ratio of 5 females:1 male). The total length and weight of the animals did not vary significantly during the year, the females had an average length of 21,867 ± 1.55 cm and an average weight of 118.63 ± 23.4 g. The males had average length of 20.353 ± 1.39 cm and an average weight of 96.90 ± 20.2 g. Females and males were in developing phases during fall and winter, and Spawning Capable in spring and summer. Spawning Capable females were collected in the fall. The closed fishing season determined for the species does not fully cover its reproductive period. This associated with the imbalance of the sex ratio, and over‐fishing of the species may be leading the species population to decline upstream of the Tucuruí reservoir on the Tocantins River.