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This study aimed to describe reproductive ecology based on morphological aspects of Peckoltia oligospila in stream rapids, eastern Amazon. A total of 186 fish (75 males and 111 females) were collected. The sex and gonadal maturity stage of these specimens were obtained based on histological characteristics of the gonads. The sex ratio, gonado‐somatic index (GSI), relative frequency of the different maturity stages, size at first sexual maturation, condition factor of the population, and fluviometry were evaluated during the study. There was a significant female frequency during the study. The population exhibited positive allometric growth without differences between sexes. GSI and relative frequency showing a reproductive period synchronized in February, and the species exhibited parcelated spawning. L50 was estimated at 5.85 and 7.39 cm for females and males, respectively. There were significant differences in the condition factor only in females that showed a highest value in August. Thus, based on the results P. oligospila has an intermediate strategy between the opportunistic and equilibrium strategies. [ABSTRACT FROM AUTHOR]

The Amazon rainforest has experienced rapid land‐use changes over the last few decades, including extensive deforestation that can affect riparian habitats and streams. The aim of this study was to assess responses of stream fish assemblages to deforestation and land cover change in the eastern Amazon. We expected that percentage of forest in the catchment is correlated with local habitat complexity, which in turn determines fish assemblage composition and structure. We sampled 71 streams in areas with different land uses and tested for relationships between stream fish assemblages and local habitat and landscape variables while controlling for the effect of intersite distance. Fish assemblage composition and structure were correlated with forest coverage, but local habitat variables explained more of the variation in both assemblage composition and structure than landscape variables. Intersite distance contributed to variance explained by local habitat and landscape variables, and the percentage of variance explained by the unique contribution of local habitat was approximately equivalent to the shared variance explained by all three factors in the model. In these streams of the eastern Amazon, fish assemblages were most strongly influenced by features of instream and riparian habitats, yet indirect effects of deforestation on fish assemblage composition and structure were observed even though intact riparian zones were present at most sites. Long‐term monitoring of the hydrographic basin, instream habitat and aquatic fauna is needed to test for potential legacy effects and time lags, as well as assess species responses to continuing deforestation and land‐use changes in the Amazon. [ABSTRACT FROM AUTHOR]

Reduced-impact logging (RIL) has been considered as the main activity of forestry management in the Amazon. However, little is known of the effects of RIL on the region's ecosystems or in their biodiversity, and such information would be useful to inform forest management. Accordingly, this study aimed to investigate the effects of RIL on physical habitat and fish assemblages in Eastern Amazonia streams. We predicted that changes caused by RIL affect stream habitat, leading to a loss of diversity and changes in species composition with a predominance of generalist species., We sampled 13 streams in basins dominated by native vegetation without evidence of logging activity (unlogged areas) and 23 in areas that had been logged at different times between 2001 and 2011. Stream physical habitat structure was characterized using a standardized protocol, and the abundance, richness and composition of fish assemblages were assessed., Biotic and abiotic data were compared between unlogged and logged areas, and among streams in areas with different logging years. The relationship between the stream habitat structure and fish assemblages was assessed using a distance-based linear model using a forward procedure, followed by application of the Akaike information criterion., Variations in tree canopy cover, channel morphology, water temperature and dissolved oxygen and conductivity accounted for most of the differences in habitat characteristics between unlogged and logged areas. A total of 53 fish species was collected, belonging to 20 families and 6 orders. Fish abundances did not vary consistently between streams in unlogged areas and those that had undergone RIL, and showed minor evidence of species-specific changes in response to logging years. Likewise, there were no obvious differences in species richness, composition and biomass between logged and unlogged sites, regardless of logging years., RIL in Eastern Amazonia is performed in compliance with technical guidelines, but this practice has resulted in changes in stream physical habitat. Nonetheless, in the headwater streams that we sampled, the effects of RIL on fish assemblages were minor. [ABSTRACT FROM AUTHOR]

A new species of Microsternarchus is described from clear water streams in the lower Rio Amazonas basin, Brazil, increasing the known species in the genus to three. The new species is distinguished from congeners by a unique set of characters including an elongated caudal filament (35.1-36.8% of the total length) and distinct irregular suborbital blotches. A dichotomous key to the species of Microsternarchus is provided.