Fish Assemblages in an Urbanized Neotropical Basin: Influence of Environmental Factors Across Dry and Rainy Periods

ABSTRACT

This study investigated the effects of season and environmental disturbances on fish communities in neotropical rivers of the Sorocaba basin, a Sub‐Basin of the Paraná River in Southeast Brazil, based on sampling 1196 individuals from 49 species, including two non‐native and one threatened with extinction. Greater richness and abundance were recorded in the rainy season, but the community structure remained stable between periods, indicating resilience to climatic variations. The rivers showed marked differences: the Sorocaba River stood out for its high diversity and low dominance, while the Una River exhibited the lowest richness and highest dominance, reflecting a gradient of anthropogenic impact. Variables such as riparian vegetation, fast flow, and substrates exerted a greater influence on species distribution than seasonality. Larger rivers supported greater abundance, but habitat degradation, especially the loss of riparian vegetation, threatens local biodiversity. Despite advances in sanitation, problems such as pollution and the presence of invasive species persist. Conservation should prioritize protecting riparian vegetation, maintaining habitats with fast flow and diverse substrates, and managing non‐native species. The observed stability is maintained by generalist species and preserved riparian forest stretches, yet anthropogenic pressure remains the main risk to the fish fauna. Integrated management measures are urgently needed to reconcile anthropogenic use of water resources and the preservation of these neotropical rivers.