TROPHIC ECOLOGY OF THE FISH IN THE RIO DOS VEADOS (UPPER PARANAPANEMA RIVER, SP) DURING THE DRY AND RAINY SEASONS

Resumo

The aim of this study was to evaluate the trophic ecology of the principal species of fish (Astyanax altiparanae, A. fasciatus, Bryconamericus stramineus, B. iheringii, Cheirodon stenodon, Characidium fasciatum, Geophagus brasiliensis, Hyphessobrycon anisitsi, Piabina argentea and Steindachnerina insculpta) captured in the littoral region of the Rio dos Veados (23º16’80’’S/48º38’67’’W), an affluent of the Rio Paranapanema, SP. The collections were conducted monthly with a seine-type trawling net with a 5.0mm mesh size, taking place between August, 1996 and December, 1997. This collection time was subdivided into the dry (April to September) and rainy (October to March) seasons. The food contents were analyzed by a volumetric method, and the food overlap determined by the Morisita-Horn index. The ten species of fish consumed different food resources, which varied in abundance (volume percentage): detritus/sediment (30.0%), aquatic insects (23.4%), microcrustaceans (17.6%), terrestrial insects (13.9%), higher plants (6.2%), algae (5.6%), fish (1.8%), and macroinvertebrates and microinvertebrates grouped together (1.5%). Patterns of similarity among the species were constructed utilizing Detrended Correspondence Analysis (DCA) with removal of the arch effect and tested by analysis of variance (unifactorial ANOVA), showing that there was no significant variation in the composition of food resources utilized by the species during the dry and rainy seasons. The main  resources consumed by the ten species were classified into three trophic categories: omnivores, detritivores and insectivores. Interspecies food overlap revealed indices of 0.059 to 0.961, showing it to be independent of the period studied, since the resources utilized were similar, both in qualitative and quantitative terms. Intraspecies food overlap in the different periods was minimal for A. altiparanae (0.662) and maximal for S. insculpta (1.0). The species studied showed little variation in relative length of intestine, with the exception of S. insculpta which had an elevated intestinal index. The variations in food resources utilized between the periods were of little relevance, indicating that the temporal factor did not influence the resources utilized by the species studied. Of the ten species  studied, nine could be viewed as generalists, considering the food resources utilized during the two periods, and only  S. insculpta behaved as a specialist.