Abstract Aquatic macrophytes are the main autochthonous component of primary production in the Amazon Basin. Floating meadows of these plants support habitats with highly diverse animal communities. Fishes inhabiting these habitats have been assumed to use a broad range of food items and compose a particular food web. We employed carbon (δ13C) and nitrogen (δ15N) stable isotope analysis to draw the trophic structure of these habitats and to trace the energy flow by its trophic levels. Fishes and other animals from 18 independent macrophyte meadows of a floodplain lake of the Solimões River (Amazonia, Brazil) were analyzed. The food web of macrophyte meadows consists of four trophic levels above autotrophic sources. In general, primary consumers exhibited a broader range of food sources than the upper trophic levels. Some fish species depended on a large number of food sources and at the same time are consumed by several predators. The energy transfer from one trophic level to the next was then mainly accomplished by these species concentrating a high-energy flux and acting as hubs in the food web. The broad range of δ13C values observed indicates that the organisms living in the macrophyte meadows utilize a great diversity of autotrophic sources. Basin communities δC δ C (δ13C δ15N δN N (δ15N 1 Amazonia, Amazonia (Amazonia Brazil analyzed general predators highenergy high

RESUMO O gênero Cichla é bastante diverso, com 16 espécies descritas. Algumas espécies são externamente muito similares e sua discriminação pode ser bastante difícil. Ao mesmo tempo, a discriminação de estoques pesqueiros é essencial para propostas de manejo. Análises morfométricas em otólitos têm sido utilizadas com sucesso para a distinção de espécies e estoques pesqueiros, principalmente em ambientes marinhos. Este estudo avaliou se o formato do otólito sagittal pode ser utilizado para discriminar entre espécies Cichla temensis, C. monoculus e C. orinocensis, bem como dentro de populações de C. temensis em diferentes rios amazônicos. Índices de forma e coeficientes de Fourier foram utilizados para descrever a forma dos otólitos. Dentre as espécies, a morfologia do otólito sagittal do C. temensis mostrou ser totalmente distinta das espécies C. monoculus e C. orinocensis. Enquanto no grupo das populações de C. temensis, os indivíduos dos rios Negro e Jatapú mostraram-se diferentes independente dos métodos utilizados. Esses resultados confirmam a capacidade de diferenciação de espécies e populações através da morfologia dos otólitos. No entanto, são necessárias mais pesquisas para verificar o papel dos efeitos genéticos em comparação aos efeitos ambientais e bióticos para explicar a discriminação observada nos otólitos.

ABSTRACT The genus Cichla is a highly diverse group, with 16 species already described. Externally, some species are very similar and discriminating between them may be very difficult. Nevertheless, discrimination of fish stocks is essential for management purposes. Morphometric analyses of otoliths have been successfully used to distinguish species and fish stocks, especially in marine environments. This study evaluated whether sagittal otolith shape can be used to discriminate among the species Cichla temensis, C. monoculus, and C. orinocensis, as well as within populations of C. temensis in rivers of the Amazon. Shape indices and Fourier coefficients were used to describe the shape of the otoliths. Among the groups of species, the morphology of the sagittal otolith of C. temensis was totally distinct from the species C. monoculus and C. orinocensis. While among populations of C. temensis, individuals from the Negro and Jatapú Rivers were different, regardless of the methods used. These results confirm the ability to differentiate species and populations by using the morphology of otoliths. However, more research is needed to verify the role of genetic versus environmental and biotic effects, and thus be able to explain the discrimination observed in otoliths.

Avaliamos a diversidade e a distribuição de espécies de peixes em dois habitats: floresta alagada e água aberta de lagos do rio Negro. Três amostragens foram realizadas em quatro lagos do Arquipélago de Anavilhanas, em 2009 e 2010. Em geral, a diversidade de espécies foi maior na floresta alagada e durante a noite. A análise de correspondência indicou que predadores estavam mais ativos a noite nos dois habitats. Onívoros, filtradores e detritívoros foram mais capturados durante o dia.

We evaluated diversity and distribution of fish species in two habitats: flooded forest and open water of lakes of Rio Negro. Each of four lakes within the Anavilhanas Archipelago was sampled three times from 2009-2010. Species diversity generally was higher in flooded forests and at night, according to correspondence analysis. Predators were most active at night, but showed no preference between the flooded forest and open water habitats. Omnivores, filter feeders, and detritivores were most active during the day.