Abstract
In order to verify the carbon source and trophic position of the main species of fishes, of the Paraná River floodplain, we analysed the proportion of stable carbon (delta 13C) and nitrogen (delta 15N) isotopes in muscle of fishes sampled in the rainy season. We analyzed adult individuals of Loricariichthys platymetopon, Schizodon borellii, Leporinus lacustris, Auchenipterus osteomystax, Iheringichthys labrosus, Leporinus friderici, and Serrasalmus marginatus. These data were compared with the results obtained by the analyzing stomach contents. The primary producers found in the Baía River were the C3 plants (riparian vegetation, macrophytes, periphyton, and phytoplankton) and the C4 plants (macrophytes). The results of the contribution analysis revealed that the carbon used by the species was derived from C3 plants. According to the trophic position estimates (diet and delta 15N), the species primarily consumed Loricariichthys platymetopon, Schizodon borellii, Leporinus lacustris, and Leporinus friderici and, secondarily Auchenipterus osteomystax, Iheringichthys labrosus, and Serrasalmus marginatus. There was no significant difference between the two methods utilized.
Highlights
Primary production in the Paraná River floodplain is supported by three main plant groups: C3, C4, and CAM (Lopes, 2001)
The combined use of stable isotopes contributes in identifying the original organic nutrient sources in complex food webs (Jennings et al, 1997; Magnusson et al, 1999; Thomas & Cahoon, 1993), which have been directly related to assimilation, the natural proportions of stable isotopes in animal tissue reflect diet in a predictable way (De Niro & Epstein, 1978; Fry, 1988)
Fishes The highest δ13C isotopic variability was verified for the species L. lacustris (–25.5 to –33.2‰) and L. platymetopon (–22.2 to –30.1‰) while the lowest was identified for L. friderici (–26.4 to –30.23‰)
Summary
Primary production in the Paraná River floodplain is supported by three main plant groups: C3, C4, and CAM (Lopes, 2001). The C plant group is constituted only by some species of aquatic macrophytes, which occur sporadically, while the CAM plant group is abundantly distributed all over the floodplain, represented by few species (Lopes, 2001). The combined use of stable isotopes contributes in identifying the original organic nutrient sources in complex food webs (Jennings et al, 1997; Magnusson et al, 1999; Thomas & Cahoon, 1993), which have been directly related to assimilation, the natural proportions of stable isotopes in animal tissue reflect diet in a predictable way (De Niro & Epstein, 1978; Fry, 1988). As a result of fractionation during food assimilation, the 15N isotope becomes enriched in relation to the 14N (De Niro & Epstein, 1981). The δ15N changes consistently along the food web, allowing inferences about the trophic position of consumers
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