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ABSTRACT. Very little research has been conducted on the swimming capacity of Neotropical fish. The few studies available have focused on large migratory species. The present study used fixed and increasing velocity tests to determine prolonged and sustained speeds of the "pequira", Bryconamericus stramineus Eigenmann, 1908, a small, abundant species found in fish passages implemented at the Paraná basin, Brazil. The results of increasing velocity tests showed significant relationships between critical speeds, total and standard lengths, and body weight. When compared with other Neotropical fish, the "pequira" is able to swim faster than individuals of other species of similar length. The point of change from sustained to prolonged swimming was found to occur at an approximate speed of 8.7 lengths per second. These data provide guidance and criteria for design and proper maintenance of structures such as fishways, fish screens and other systems that aim to facilitate or avoid upstream passages as part of management strategies.

Several hypotheses are used to explain species richness patterns. Some of them (e.g. species-area, species-energy, environment-energy, water-energy, terrestrial primary productivity, environmental spatial heterogeneity, and climatic heterogeneity) are known to explain species richness patterns of terrestrial organisms, especially when they are combined. For aquatic organisms, however, it is unclear if these hypotheses can be useful to explain for these purposes. Therefore, we used a selection model approach to assess the predictive capacity of such hypotheses, and to determine which of them (combined or not) would be the most appropriate to explain the fish species distribution in small Brazilian streams. We perform the Akaike’s information criteria for models selections and the eigenvector analysis to control the special autocorrelation. The spatial structure was equal to 0.453, Moran’s I, and require 11 spatial filters. All models were significant and had adjustments ranging from 0.370 to 0.416 with strong spatial component (ranging from 0.226 to 0.369) and low adjustments for environmental data (ranging from 0.001 to 0.119) We obtained two groups of hypothesis are able to explain the richness pattern (1) water-energy, temporal productivity-heterogeneity (AIC = 4498.800) and (2) water-energy, temporal productivity-heterogeneity and area (AIC = 4500.400). We conclude that the fish richness patterns in small Brazilian streams are better explained by a combination of Water-Energy + Productivity + Temporal Heterogeneity hypotheses and not by just one.

This book is dedicated to the memory of our friend Volney Vono. We miss him, his funny stories, and his ecological knowledges.