Basin-scale eDNA metabarcoding reveals freshwater fish biodiversity patterns across major river systems in Türkiye

Area of Science:

• Freshwater ecology and ichthyology
• Environmental DNA (eDNA) metabarcoding applications
• Biodiversity assessment and conservation science

Background:

• Global freshwater fish biodiversity is declining due to multiple anthropogenic pressures.
• Türkiye's rich freshwater fish fauna is underrepresented in large-scale biodiversity assessments.
• Environmental DNA (eDNA) metabarcoding offers a scalable, non-invasive method for biodiversity surveys.

Purpose of the Study:

• To conduct the first nationwide, basin-scale eDNA metabarcoding survey of freshwater fishes in Türkiye.
• To establish a molecular baseline for Turkish freshwater ichthyofauna.
• To assess the utility of eDNA metabarcoding for detecting cryptic and rare species.

Main Methods:

• Collected triplicate water samples from 29 sites across seven major Turkish river basins (>6000 km transect).
• Utilized high-throughput sequencing of the mitochondrial 12S ribosomal RNA (rRNA) gene for eDNA analysis.
• Analyzed 351,392 high-quality reads to identify fish species present in the sampled river systems.

Main Results:

• Detected 52 fish species, including native, invasive, and previously unrecorded taxa within their basins.
• The Eastern Mediterranean basin showed the highest species richness (28 species) and diversity.
• Beta-diversity analyses indicated significant spatial structuring and biogeographic separation among basins.

Conclusions:

• eDNA metabarcoding successfully uncovered cryptic and low-abundance fish taxa missed by conventional surveys.
• This study provides a crucial molecular baseline for Turkish freshwater ichthyofauna.
• Large-scale eDNA surveys are powerful tools for transforming freshwater biodiversity monitoring and conservation.