Abstract
ABSTRACT This study was carried out in a section of the middle course of the Teles Pires River, a clear water river that drains ancient and highly eroded geological formations, and where five hydropower plants are planned or in construction. In this study we tested the hypothesis that local fish fauna is mainly sustained by autochthonous food resources, with modest changes in the trophic structure of fish assemblages along the hydrometric cycle. Sampling was performed every three months between July 2008 and May 2009 at seven sites distributed along a 50-km section of the river. Piscivores was the most representative group in terms of biomass, abundance and species richness, followed by herbivores, insectivores and omnivores. The trophic structure did not change significantly during the hydrometric cycle, only omnivores showed significant temporal variation in abundance. The main food resources consumed by the ichthyofauna were of autochthonous origin, mainly immature aquatic insects and fish. Eight of 34 species showed temporal variations of the food resources consumed. Our results corroborate the hypothesis that the fish fauna of large, clear water rivers can be sustained by autochthonous resources. This contributes to understanding some determinants of fish production in large Neotropical rivers.
Highlights
Given the importance of estimating and predicting fish biomass, fishery sustainability, and understanding fish diversity, larger rivers are often the focus of trophic ecology studies
Based on diet information (Tab. 1), the fish species were classified into seven trophic categories: carnivores, species that consumed fish and aquatic and/or terrestrial invertebrates without predominance of any item; detritivores, species that consumed mainly particulate organic material in different stages of decomposition together with mineral particles; herbivores, represented by species that consumed terrestrial and/or aquatic vascular plant material, and/or algae; insectivores, species that predominantly consumed aquatic insects and secondarily by species that consumed mainly terrestrial insects; invertivores, the ones which consumed insects as well as other invertebrates with no predominance (IAi ≥ 50%) of one type; omnivores, consumed items of both vegetal and animal origins in similar proportion; piscivores, which ingested whole fish or pieces of muscle or fins and scales
Aquatic insects and fish were the most important items in fish diets (Tab. 1 and Appendix S3 - Available only as online supplementary file accessed with the online version of the article at http://www.scielo.br/ni)
Summary
Given the importance of estimating and predicting fish biomass, fishery sustainability, and understanding fish diversity, larger rivers are often the focus of trophic ecology studies. Due to the usual high biomass and diversity of fishes, large rivers in the Neotropical region provide a good opportunity to understand processes related to secondary production (Roach, 2013; Humphries et al, 2014). Low turbidity throughout the hydrometric cycle is a remarkable characteristic of clear water rivers draining the Brazilian and Guiana Shields in the Neotropical region Few studies in these rivers have focused on the origin of resources sustaining fish fauna while considering the seasonal variation. ZuluagaGómez et al (2016), using stable isotopes and suggest that clear water rivers are mainly sustained by autochthones sources; but the effect of seasonality was not considered in the study
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