Influence of a large dam and importance of an undammed tributary on the reproductive ecology of the threatened fish matrinxã Brycon orthotaeniaGünther, 1864 (Characiformes: Bryconidae) in southeastern Brazil , when compared with the site 1.In site 2 was registered the highest GSI means (9.97 ± 2.96 for females and 0.93 ± 0.52 for males), compared with the site 1 means. Reproduction period occurred from October to February. Unlike site 2, no spawned females or spent males were captured in site 1. Significant differences were found between females and males in site 2 (χ 2 = 26.84, df = 1, P < 0.05). Physical-chemical parameters of the water presented higher values in site 2. The canonical correlation test indicated that the reproduction of males is less susceptible to environmental factors than that of females. These results show that B. orthotaenia finds favourable conditions to reproduction just in site 2.Um total de 312 adultos de matrinxã foram capturados bimestralmente entre 2011-2012, em dois pontos do rio São Francisco: imediatamente a jusante da barragem de Três Marias (ponto 1) e na confluência com o rio Abaeté (ponto 2). Exemplares de Brycon orthotaenia do ponto 2 apresentaram maiores valores de comprimento total (32,24 ± 5,70 cm para fêmeas e 26,64 ± 3,79 cm para machos) e peso corporal (506,66 ± 332,17 g para fêmeas e 267,36 ± 145,84 g para machos) quando comparado com peixes do ponto 1. No ponto 2, foi registrado as maiores médias de IGS (9,97 ± 2,96 para fêmeas e 0,93 ± 0,52 para machos) em comparação com o ponto 1. O período reprodutivo ocorreu de outubro a fevereiro. Ao contrário do ponto 2, fêmeas desovadas e machos espermiados não foram capturados no ponto 1. Foram encontradas diferenças significativas entre fêmeas e machos no ponto 2 (χ 2 = 26,84, gl = 1, P < 0,05). Parâmetros físico-químicos da água apresentaram maiores valores no ponto 2. A análise de correlação canônica indicou que a reprodução de machos é menos susceptível a fatores ambientais do que de fêmeas. Estes resultados mostram que B. orthotaenia encontra condições favoráveis para a reprodução apenas no ponto 2.

Downstream impacts of dams on fish fauna are poorly studied, despite causing thermal and hydrological changes that affect the reproductive activity of the fish community. The present study aims to evaluate the reproduction of Leporinus reinhardti in 2 sections of the São Francisco River, Brazil, downstream from the Três Marias Dam. Section 1 (S1) is the first 34 km downstream from Três Marias Dam and section 2 (S2) is 34 to 54 km downstream from the dam, where the São Francisco River receives a mid-sized tributary called the Abaeté River. In S1, the values of temperature, dissolved oxygen and flow were lower than those obtained in S2. In S1, females and males did not complete reproduction, a fact proven by the absence of spawned females and males. In S2, reproductive success was proven due to the presence of spawned females and males. Furthermore, the values of total length, body weight, gonadosomatic index, fecundity and vitello genic oocytes were statistically higher than those obtained in S1. The canonical correlation test indicated that the reproduction of females is more dependent on environmental factors than that of males. In S2, L. reinhadti found appropriate conditions for reproduction, probably influenced by the Abaeté River, confirming the need of preserving this tributary for the reproductive success of this species.

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