The role of sediment on the energy availability for fishes in the upper Paraná river floodplain - doi: 10.4025/actascibiolsci.v34i4.9335

This study aimed to identify potential sources of organic matter in sediment, using stable isotopes of carbon (delta13C) and nitrogen (delta15N). Sediment samples were gathered from the margin and in center of three subsystems: Ivinheima, Paraná and Baia, in August/2001. The samples were fractionated granulometrically and separated by size ( 200 µm; 70-200 µm; > 70 µm), prepared and sent to CENA / USP, for identifying the isotopes proportions. Significant differences were detected in the isotopic ratios of the sediment only between sampling stations. The Baía channel presented the lowest delta13C values, while the highest ones were recorded in Paraná river. At this last, delta15N values were negative (-14.41). We did not verify significant difference in isotopic composition between the particle sizes of sediment, and between the sampling points. The main sources of carbon for the sediment were C3 macrophytes, periphyton and particulate organic carbon (POC).

Availability of sedimentary organic matter for benthic fishes of the upper Paraná river floodplain - DOI: 10.4025/actascibiolsci.v26i2.1634 / Disponibilidade de matéria orgânica sedimentar para peixes benticos da planície de inundação do rio Paraná - DOI: 10.4025/actascibiolsci.v26i2.1634

This work aims to investigate the hypothesis that sedimentary organic matter presents concentration variations in accordance to the size of sediment particles and to proximity with the river"s margin. This organic matter is known as a feeding source for benthonic fishes. Sampling of the sediment was carried out in dry and rainy periods, at three Paraná River floodplain subsystems. Three sampling points were established: right margin, center and left margin. The samples (n = 88) were submitted to granulometric fractionation ( 70µm; between 70 and 200µm; > 200µm). Low variability in organic matter concentration was observed for samples from the center of the subsystems. Particles, smaller than 70µm, had high variability in organic matter concentration. The rainy period was shown to affect concentration of organic matter adhered to the sediment fractions in transversal section at the sampled environments. With support of literature, the experiment lead to the conclusion that fish species which ingest particles of detritus 70µm obtain more organic matter of sediment

O presente trabalho teve por objetivo investigar a hipótese de que o material orgânico sedimentar, conhecida fonte de alimento para espécies de peixes exploradores de fundo, apresenta variações na concentração de acordo com o tamanho das partículas do sedimento e proximidade com a margem do rio. A obtenção das amostras de sedimento foi realizada no período de seca e de chuva em três subsistemas da planície de inundação do rio Paraná, sendo estabelecidos três pontos de coleta: margem direita, centro e margem esquerda. As amostras (n=88) foram submetidas ao fracionamento granulométrico ( 70µm; entre 70 e 200µm; > 200µm). Observou-se menor variabilidade na concentração de matéria orgânica para as amostras do centro e maior para partículas menores que 70µm. Identificou-se o efeito do período de chuvas sobre a concentração de matéria orgânica aderida as frações de sedimento das secções transversais e nos ambientes amostrados. Concluiu-se, com base na literatura, que as espécies de peixes que ingerem detrito com partículas 70µm, obtêm mais matéria orgânica do sedimento