The use of fish diversity and abundance as environmental indicators in a mining region in Brazilian Amazonia

The impacts of mining on aquatic biodiversity pose significant challenges for environmental mitigation, particularly near protected areas. This study assessed fish abundance and diversity (assemblage composition, alpha and beta diversity, indicator species, and Species Contribution to Beta Diversity – SCBD) in the Itacaiúnas and Parauapebas river basins, Brazilian Amazonia, across dry and rainy seasons. We hypothesized that basins near mining-impacted areas would exhibit reduced fish abundance and diversity compared to control areas. To test this, four sampling points were established per basin (two controls, two impacted), totaling eight sites, where fish were collected using gillnets and physicochemical water parameters were simultaneously recorded. Fish abundance and alpha diversity peaked during the rainy season but showed no significant differences between control and impacted areas. However, beta diversity was highest in the Parauapebas basin, and distinct indicator species emerged: Plagioscion squamosissimus and Pygocentrus nattereri were associated with control areas, while Satanoperca jurupari characterized impacted sites. A Redundancy Analysis (RDA) linked environmental variables (temperature, salinity, conductivity) to species distributions, reflecting water quality influence. Our data suggest that phenotypic plasticity might mask mining's negative effects by favoring generalist species. While abundance and richness did not clearly differentiate areas, beta diversity patterns and indicator species highlight the critical need for continuous, integrated monitoring to assess long-term ecological shifts.