<b>Strategic collection lights up global freshwater fish diversity darkspots with minimal cost</b>

<b>Significance Statement:</b>Fundamental gaps persist in describing, mapping, and sequencing freshwater fish species, limiting effective biodiversity assessment and conservation actions. We quantified these taxonomic, geographic, and genetic knowledge shortfalls across 3,364 global drainage basins, identifying hotspots of undocumented freshwater diversity and uncovering their underlying socioeconomic drivers. By integrating multi-objective optimization, our study pinpoints regions, especially large tropical rivers, where strategic data collection could yield maximal biodiversity impact with minimal cost. This approach provides an actionable blueprint for systematically bridging global freshwater biodiversity gaps, balancing urgency, feasibility, and conservation value, ultimately advancing comprehensive global biodiversity documentation and freshwater conservation goals.<b>Supporting Information:</b>Table S1. Comprehensive list of the 18,821 valid freshwater fish species included in this study (updated 24 November 2024)Table S2. List of 395 drainage basins identified as freshwater fish biodiversity darkspots across eight shortfall scenariosR code used in this study, along with data process and manipulation files, is available on GitHub at https://github.com/Otoliths/FW_Fish_Darkspot<br>