Impoverished fish assemblages of temperate Neotropical streams respond to environmental degradation and support a sensitive Index of Biotic Integrity

Fish as bioindicators are a widely used tool for environmental monitoring of freshwater ecosystems worldwide. However, its adaptation to temperate Neotropical streams constitutes a challenge due to the presence of pauperised ichthyofauna with high tolerance to environmental degradation. We designed, evaluated, and validated an Index of Biotic Integrity (IBI) that uses fish as bioindicators of the ecological integrity of streams of the Pampa Plain, Argentina. An integral characterization of the environmental conditions (water quality, habitat structure, and riparian condition) and fish assemblages were performed in 17 study sites (natural grasslands, urban, and livestock reaches). The IBI was designed with 10 metrics and showed to be sensitive to different environmental conditions due to significant differences between study sites and land uses. The IBI also showed to be responsive due to its significant associations with water quality, habitat structure variables, and some multimetric indexes. Moreover, when validated against a recently fish database, it demonstrated to be sensitive for use in other temperate streams exposed to similar environmental conditions. An integral environmental assessment as the one designed can lead to optimized strategies for the management and conservation of these fragile ecosystems.