author(s)
Saokat Ahamed, Md. Shajamal, Neaz Al Hasan, Khondaker Rashidul Hasan, Parvez Chowdhury, Md. Abu Kawsar, Parvin Akhter and Maliha Hossain Mou

abstract
The study was conducted in the Kharkharia-Tilai River in the Northern part of Bangladesh to assess the present status of fish biodiversity. To study the fish biodiversity, fish samples were collected from January to September 2019. A total of 57 species belonging to 20 families was recorded of which cypriniformes were found to be most dominant order during the study period. Out of 57 species cypriniformes were 32 species and then siloriformes (13), perciformes (10) and others. The value of H ranged from 0.40 (March) to 0.95 (October), D varied from 3.29 (March) to 6.48 (October), and e ranged from 6.89 (October) to 1.00 (May and June).H and D values showed that the diversity of fish fauna was the highest within the month of October. Among the total 56 fish species of Tilai rivers which of them 8.92% was endangered, 10.71% vulnerable, 16.07% near threatened, 62.5% least concern and 1.78% were data deficient. However, fish species diversity of Tilai river were decreasing day by day due to siltation, pollution, constructions of obstacles for fish movement.