Environmental DNA (eDNA) based fish biodiversity assessment of two Himalayan rivers of Nepal reveals diversity differences and highlights new species distribution records

Although over 180 freshwater fish species have been reported from Nepal, little is known of their ecology and distribution. This information needed because diversity may be threatened by developments like hydropower constructions. We conducted Nepal’s first environmental DNA (eDNA) based biodiversity assessment in two major river systems- Karnali River (KR), which still pristine Trishuli (TR) with numerous plants. The eDNA was concentrated filtering (0.45 μm pore size) liters water collected at different sampling points each study site. A total 224 samples (KR = 162 TR 62) were collected, identified 12S rRNA metabarcording approach utilizing Illumina sequencing platform. Alpha beta between basins compared. Also, KR site, (N 795) caught, using COI gene barcoding method- building reference database. Field 21 through morphology barcoding, where Barilius spp. Schizothorax the most abundant. From 244 samples, 24 Operational Taxonomic Units (OTUs) 46 19 being common to both sites, 27 unique KR, five only. Most fishes Cypriniformes Siluriformes orders, Long distance migratory ( Tor spp, Neolissochilus hexagonolepis ) non-native as well. significantly lower than KR. High sites indicated low similarity demonstrated utility a non-invasive technique for particularly useful areas Nepal scarce data on