Ichthyofaunal diversity of river Kulik and Nagar, two connected transboundary rivers between India and Bangladesh

Abstract

The transboundary rivers of North Bengal, including the Kulik and Nagar rivers, play a vital role in supporting regional freshwater biodiversity and sustaining local livelihoods. However, these rivers face escalating threats from anthropogenic activities and environmental changes. This study provides a comprehensive assessment of ichthyofaunal diversity in the Kulik and Nagar rivers, both part of the Mahananda River Basin, using year-round field surveys conducted in 2022. A total of 81 fish species belonging to 32 families were documented, with 72 species common to both rivers, indicating high similarity in species composition. The Cyprinidae family dominated both rivers, followed by Danionidae and Bagridae. Three exotic species and several species of conservation concern were recorded, including one Endangered, two Vulnerable, and five Near Threatened species as per IUCN status. Diversity indices and Bray-Curtis similarity analyses revealed largely comparable alpha and beta diversity patterns between the rivers. Taxonomic distinctness indices further supported stable and balanced community structures. The presence of rare, endemic, and habitat-sensitive taxa underscores the ecological significance of these rivers. Given the increasing anthropogenic pressures and the ecological value of these systems, the study highlights the urgent need for cross-border conservation strategies and sustainable riverine biodiversity management.