The aim of this study was to assess the ecomorphological patterns and diet of four Characiformes fish species in a poorly physically structured tropical reservoir. We tested the hypothesis that body shape and diet are associated, because environmental pressure acts on the phenotype, selecting traits according to the available resources. Ten ecomorphological attributes of 45 individuals of each species - Astyanax cf. bimaculatus (Linnaeus, 1758), Astyanax parahybae Eigenmann, 1908, Oligosarcus hepsetus (Cuvier, 1829), and Metynnis maculatus (Kner, 1858) - , collected between February and November 2003, were analyzed, and the patterns were assessed using Principal Components Analysis (PCA). Diet similarity among fish species was assessed using cluster analysis on feeding index. The first two axes from PCA explained 61.73% of the total variance, with the first axis being positively correlated with the compression index and relative height, whereas the second axis was positively correlated with the pectoral fin aspect. Two well-defined trophic groups, one herbivorous/specialist (M. maculatus) and the other formed by two omnivorous/generalist (A. cf. bimaculatus, A. parahybae) and one insectivorous-piscivorous (O. hepsetus) were revealed by the cluster analysis. Astyanax. cf. bimaculatus and A. parahybae differed. The first has comparatively greater relative height, relative length of the caudal peduncle and lower caudal peduncle compression index. However, we did not detect a close correspondence between diet and body shape in the reservoir, and inferred that the ecomorphological hypothesis of a close relationship between body shape and diet in altered systems could be not effective.

Efeito do tempo de conservação dos espécimes sobre a qualidade dos microincrementos em otólitos sagittae de Anchoa tricolor (Agassiz) (Clupeiformes, Engraulidae). O número de microincrementos em otólitos sagittae de espécimes de pós-larvas de Anchoa tricolor (Agassiz, 1829) fixadas em formol 10% foram comparados em diferentes períodos de conservação (quatro dias versus quatro anos). Diferenças significativas foram encontradas no número de microincrementos para pós-larvas variando de 20-26 mm de comprimento total (CT), com médias de 18,6 microincrementos (± 0.75 erro padrão) para peixes preservados por quatro anos, e 35,3 microincrementos (± 1.28 erro padrão) para peixes preservados por quatro dias. Portanto, o número de microincrementos em otólitos de pós-larvas preservados por longos períodos pode não ser adequado para inferências de taxas de idade ou crescimento. Adicionalmente, não foram detectados ou extraídos otólitos em pós-larvas menores do que 20 mm CT devido a maior composição de matéria orgânica durante esta fase do ciclo de vida.

We compared the number of microstructure of Anchoa tricolor (Agassiz, 1829) post-larvae sagittae otoliths in specimens fixed in formalin 10% in different periods of conservation (four days versus four years). Significant differences were found in the number of microstructure for post-larvae ranging from 20-26 mm total length (TL), with averages of 18.6 microstructures (± 0.75 standard error) for fishes preserved for four years, and 35.3 microstructures (± 1.28 standard error) for fishes preserved for four days. Therefore, the number of post-larvae otoliths microstructure preserved for long periods can not be suitable to infer age or growth rates. Additionally, we failed in detecting and extracting otoliths in post-larvae smaller than 20 mm TL preserved due to its comparatively higher organic matter composition, mainly during the early life cycle.