The biodiversity of fish in transboundary rivers from north-eastern Bangladesh

The biodiversity of freshwater fish is disappearing at an alarming rate around the globe, with transboundary rivers in Bangladesh being especially vulnerable. From October to December 2023, we surveyed the fish biodiversity of 11 transboundary rivers in north-eastern Bangladesh using the available literature and online FishBase data for species identification. We also added a small number of specimens from our previously examined samples that comprised of 74 fish species belonging to eight orders and twenty-four families. Our survey results indicate that the order Cypriniformes had the biggest number of species (38%), followed by the orders Siluriformes (30%), Perciformes (24%), Clupeiformes (3%), Synbranchiformes (1%), Beloniformes (1%), and Tetraodontiformes (1%). Less than 30% of the entire studied area had 26 fish, indicating that the fish population was confined to a relatively limited region. The total number of species was lower than that we had anticipated, which explains the declining trend of the fish biodiversity in the transboundary rivers of north-eastern Bangladesh. Our survey data have allowed us to gain some early understanding of the hidden biodiversity of fish in these rivers, which may prove useful to other researchers conducting follow-up studies. Since there is currently no published description of the ichthyofaunal diversity in transboundary rivers, the current data on 74 species of ichthyofauna will be useful to future researchers, planners, and policymakers. In order to safeguard the faunal composition of a riverine ecosystem, more efforts incorporating genetic data will be helpful in detecting the biodiversity of fish as well as the cryptic species of other transboundary riverine systems. These efforts will also reinforce the need to re-evaluate the checklist and promote sustainable conservation directions.