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Fish as sentinel species for riverine ecosystem health assessment and conservation management
Summary
This review paper shows how fish act as "canaries in the coal mine" for river health—since they absorb pollutants like heavy metals, pesticides, and microplastics from their water, scientists can study fish to catch contamination early, often before it becomes a bigger problem. This matters for us because the same rivers that harm fish often supply our drinking water and food, so healthier rivers (tracked through fish monitoring) mean lower risk of harmful chemicals and microplastics ending up in what we eat and drink.
Freshwater ecosystems are increasingly threatened by anthropogenic activities, including pollution, habitat fragmentation, hydrological alterations, climate change, and others, especially in the case of rivers. Fish occupy a range of trophic levels and possess varied sensitivities to environmental stressors, making them excellent sentinels for evaluating and monitoring the health of these dynamic ecosystems. In this context, we review the current knowledge on the integration of fish-based biomonitoring, ecotoxicological approaches, and conservation strategies, to provide a holistic framework for river ecosystem management. The paper reviews existing and emerging biomonitoring techniques, from traditional indices such as the Index of Biotic Integrity (IBI) and multimetric assessments to advanced molecular and omics tools (e.g., transcriptomics, metabolomics, and eDNA metabarcoding) that allow early detection of sublethal effects and community-level shifts. Reviews are provided on ecotoxicological perspectives, including bioaccumulation of contaminants (heavy metals, pesticides, pharmaceuticals and microplastics), biomarker responses (histopathological, physiological and genetic) and complex interactions of multiple stressors. The ways in which these data contribute to causal diagnosis of ecosystem degradation and risk assessment are considered. Moreover, the review connects monitoring science to on-the-ground conservation by showcasing successful case studies where fish sentinel data have resulted in policy changes, habitat restoration, protected area establishment and species recovery programs. Critical discussions of challenges including data standardization, integration of big data analytics, climate-induced range shifts, and the need for interdisciplinary approaches. The paper argues for a “One Health” paradigm that connects fish health, ecosystem integrity and human well-being, and suggests an integrated framework for adaptive management of river basins globally. This review highlights the importance of fish as key indicators in the transfer of scientific knowledge to successful conservation results, ultimately leading to the sustainable management and restoration of threatened freshwater ecosystems.