The fishes of the family Characidae are among the main species of fresh water fishes in South America. In this work, some aspects of the population structure of two Astyanax species were assessed. The fishes were caught in Santo Antônio and São José rivers, in the Paraguaçu basin, by standardized monthly samplings adapted to the microhabitats. Astyanax sp. b (São José river) presented larger size than Astyanax sp. a (Santo Antônio river). The length-weight relationship showed positive allometric growth for Astyanax sp. a, and negative for Astyanax sp. b. Both the species showed a long reproductive period, with higher activities in dry period.
Astyanax; Characidae; Chapada Diamantina; Paraguaçu River; population structure
