Population parameters of the red-bellied piranha Pygocentrus nattereri (Kner, 1860) (Characiformes: Serrasalmidae) of the São Miguel River, Rondônia state, Brazil

In this study, the structure and distribution of Pygocentrus nattereri populations in the São Miguel River basin, Rondônia state, Brazil, were evaluated. From August 2020 to July 2021, monthly fisheries were carried out, using gillnets with meshes ranging from 40 to 160 mm between opposite knots, which were in place for 48 hours and inspected at 6 am; 12 am; 6 pm and 12 pm. Growth parameters and mortality were estimated using length-frequency data. The population values ​​found for P. nattereri were L∞ = 29 cm, k = 0.55 .year-1, with mortality values: M = 0.57, Z = 0.98 and F = 0.41. year-1. The relationship between weight and length was described by Wt = 0.0372.Lt2.983. The data obtained indicates that the P. nattereri stocks in the study region are not overfished; therefore, measures and actions for a fishing management plan for P. nattereri populations must be implemented for the studied river region in order to prevent the increase in these populations and preserve the other species of fish commercial interest.