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Fish communities' organisation is a challenging task due to global, local and temporal variations related to biotic and abiotic factors, highlighting anthropic activities. The Verde River Basin (VRB) was chosen as a model to the fish community study due to its complexity, presenting a longitudinal gradient of degradation. The ichthyofauna and abiotic factors were sampled during twelve months in four sites. Analyses employed rarefaction curves with Hill numbers estimators and canonical correspondence analysis. The endemic Apareiodon sp. (not described), Hypostomus albopunctatus, H. strigaticeps, Oligosarcus paranensis, Neoplecostomus yapo and Trichomycterus diabolus were associated with structurally complex and well-preserved environments. In contrary, Astyanax aff. fasciatus, Corydoras ehrhardti, Geophagus brasiliensis, H. ancistroides and Phalloceros harpagos showed tolerance to impacted environments. The methods here employed allowed to identify and explain differences in the ichthyofauna structure, distinguishing the influence of spatial, temporal and human effects on the fish communities. K E Y W O R D Sabundance, anthropic impacts, diversity, entropy, lotic system | 1127 SILVEIRA Et AL.

Summary This paper presents length‐weight relationships (LWR) for 22 species from the Pitangui River Basin, Brazil. For six of these species these are the first LWR records; for nine other species these are the first LWRs recorded in FishBase.

Population dynamics provide crucial information for management and conservation. This study analysed the spatial and temporal patterns in reproductive biology, age and growth of Astyanax aff. fasciatus from a Neotropical river. Although located in a priority area for conservation, this river is affected by human activities in the surrounding landscapes. Water and environmental parameters were subjected to principal component analysis (PCA) to characterise the different sampling sites. Length–frequency distributions, gonad development and body indices were used to evaluate maturity and spawning, and to calibrate the von Bertalanffy model to determine the age and growth of A. aff. fasciatus. Reproductive behaviour of the species was not homogeneous along the river, due to geomorphology and human activities in the surrounding areas, with some sites becoming unavailable for breeding. The PCA highlighted the geomorphological, human (first axis) and temporal (second axis) trends influencing the environmental features along the river. Females predominated throughout the basin, and spawning took place from September to June in distinct areas of the river. The species matures at an age of 1–1.5 years, and so tends to be a fast-growing species, with a life span close to 3.5 years. Fish population dynamics should be monitored to support conservation and management, both for the fish species and the aquatic environments.