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Abstract: The hydrological regime represents the driver of ecological function and biodiversity in tropical river floodplains. This study aimed to document the species composition and evaluate the effect of the flood pulse on the fish community of Amapá Lake, an oxbow lake temporarily connected to the Acre River. Between October 2008 and September 2009, fish were sampled monthly with gill nets, and seven physical–chemical variables were recorded at three sampling stations along the lake. The fish community structure and physical–chemical variables were compared among the hydrological phases of pre-flooding, minor and major flood and post-flooding, and the degree of association between the limnological characteristics and species composition was explored with a canonical correspondence analysis. A total of 2131 specimens belonging to 53 species were captured. The numerical abundance and biomass of fish and water temperature were higher in the pre and post-flooding phases. Samples of the pre-flooding phase comprised more than 40% of the overall numerical abundance (115 ind. 1000m2 24h−1 ±16 se) and biomass (9949g1000m2 24h−1 ±1.816 se) due to the greater dominance of few species, mainly small (the Siluriformes Hypoptopoma gulare) to medium sized (the Characiformes Triportheus curtus) during low waters. With the onset of the minor flood, conductivity decreased and depth increased in the lake, whereas total phosphorous and pH reduced significantly at major flood. The composition and abundance of fish community changed more among hydrological phases than species richness and 26% of this annual variability in the biotic component was shaped exclusively by the physical–chemical variables. As fish community and physical-chemistry of the Amapá Lake undergo to the hydrological cycle of the Acre River, these results reinforce the general pattern of predictable seasonal alterations in the functioning of tropical floodplains. Based on the general decrease in dominance during the long flood pulse and the occurrence of piscivorous migrators among the five most abundant species, we conclude that the seasonal variation in the hydrometric level of the Acre River plays an important role in maintaining the high fish diversity observed in the Amapá Lake all year round. [Copyright &y& Elsevier]

The removal of native forest affects stream characteristics, processes, and organisms at the local scale. We compared the structure of fish assemblages between microbasins impacted by deforestation and those in pristine condition in the Amazonian Machado River basin, Brazil. Fish were collected with seine and dip nets along an 80-m stretch of 28 streams. At each site, we recorded physical, chemical, and land-water ecotone variables. We collected 6,586 specimens of 109 species, being 39 and 18 of them exclusively of forested and deforested streams, respectively. Non-significant differences were found for abundance and species richness between forested and deforested streams. A total of four main trophic groups were identified. Carnivores were more abundant in forested streams, whereas herbivores, omnivores and detritivores species were the most abundant in deforested streams. The deforested streams showed higher abundance and richness of algae and periphyton consumers, while forested streams presented higher abundance and richness of invertebrate consumers. Forested streams presented longer foodchains, higher occurrence and abundance of species that have more specialized habits and are intolerant to degraded environments, whereas generalist and tolerant species predominated in deforested streams. We conclude that species composition in Amazonian streams predictably responds to the degree of forest cover. [ABSTRACT FROM AUTHOR]

Invasive Cichla populations in the São João River basin were genetically analysed and compared with Cichla populations from other neotropical hydrographic basins. Polymorphic sequences within the mitochondrial DNA D-loop region confirmed the introduction of different populations to the regions under analysis. Cichla kelberi was introduced to the Juturnaíba reservoir and a downstream area of the São João River, with Cichla monoculus restricted to downstream river areas. Results from this study will be useful for monitoring invasive Cichla populations in the coastal basin since it elucidated the taxonomic units in the reservoir and an areas downstream. [ABSTRACT FROM AUTHOR]