Impact of the Três Marias dam on the reproduction of the forage fish Astyanax bimaculatus and A. fasciatus from the São Francisco River, downstream from the dam, southeastern Brazil

Abstract

Alterations to the hydrologic regime downstream from hydroelectric dams include thermal disturbances which may have an impact on the reproductive success of fish. In order to make a comparative analysis of forage fish reproduction in two sections of the Sao Francisco River downstream from the Tres Marias hydroelectric power plant, we captured 606 specimens of Astyanax fasciatus (n = 465) and A. bimaculatus (n = 141) at 2-month intervals between November 2009 and October 2010. Fish were captured in two sections of the Sao Francisco River: section 1, encompassing the first 34 km immediately downstream from the dam; section 2, after the confluence with the Abaete River, 34–54 km downstream from the dam. The canonical correlation test indicated that for both species, female reproduction is more dependent on environmental factors than male reproduction. Compared to section 1, the specimens captured in section 2 were more abundant and the females of both species presented larger total length, body weight, gonadosomatic index and fecundity values. Higher values of water temperature, dissolved oxygen and turbidity during the rainy season (September to February) were also recorded for section 2, when compared to section 1 where the physical–chemical conditions of the water do not favour reproduction. Based on this analysis of reproductive parameters, this study shows, for the first time, that the reproductive activity of two species of forage fishes, A. fasciatus and A. bimaculatus, from the section of the Sao Francisco River immediately downstream from the Tres Marias dam is disrupted and that the Abaete River is an important tributary for the reproductive success of these species.