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Estrutura trófica da comunidade de peixes de riachos da bacia do rio Itanhaém, litoral sul do estado de São Paulo, Brasil

2009; Linguagem: Inglês

2639-6459

André Teixeira da Silva,

Fish Ecology and Management Studies

The purpose of this study was to understand the trophic relationships which have been established for the fish species at distinct streams of the Itanhaem river basin. For this purpose the morphologic and physic-chemical properties of distinct streams were also considered. Nine distinct streams at the low flooding part of the system were sampled during two distinct field campaigns (march and november, 2006). In each of them a 50 m segment was sampled, by sampling in the sense direction from the river mouth to the water source. An electric fishing device was used to catch the fish. At the same places where fish were caught, abiotic data were also obtained: stream width, depth, current flow speed, main substrate composition, dissolved oxygen, water pH, conductivity, turbidity, water temperature, marginal vegetation, its preservation state, vegetation cover. The fish food preferential items were determined by using the Kawakami-Vazzoler Index, and the comparison for different streams and campaigns (when the stomach numbers contents were sufficient to permit analyses) was calculated by the use of the Grouping Analysis using the Simpson Index and the connection method adopted by the UPGMA. The species width niche, for each one of them was calculated using the Levins Index. The fish species were distributed at distinct trophic groups by the inspection of the predominant items, as follows: carnivorous-predator, insectivorous, herbivorous, perifitivorous, detritivorous, benthonic omnivorous and omnivorous species. The streams were classified at distinct by the use of the Non-Metric Multidimentional Scaling analysis (NMDS). The distances used for the ordenations were: Morisita Index, to verify the streams ordenation related to the proportion of the fish mass of each trophic group; the Euclidian distance to ordenate the streams in relation to the abiotic properties. The relationship between the considered variables and the obtained NMDS dimentions was verified using the Spearman Correlation Coefficient. The relationship between the biomass proportion of the trophic groups to the abiotic stream characteristics has been verified using the Canonic Correspondence Analysis (CCA). A number of 33 fish species totalizing 2081 specimens was collected. The stomach contents for 20 species were compared, totalizing 1023 stomach contents (511 from May and 512 from november). Insects were in general the most consumed items, but crustaceans, particulated material and plant items were clearly dominant items for other ones. The Levins Index showed the evidence that most species present a wide feeding spectrum, as they consume diversified food categories, within the intrinsic limit a species may display in its own food variety possibility. Some individuals belonging to a same species varied their food consume, according to the stream they were found, while other ones showed