Rita Choudhury1, Puranjit Das2* 1Department of Zoology, Tihu College, Tihu, Nalbari-781371, Assam, India 2Department of Zoology, Bhattadev University, Bajali, Pathsala-781325, Assam, India Abstract Tenualosa ilisha, an anadromous fish, inhabited in the lower region of the estuaries and the foreshore areas migrating to river for spawning. The Hilsa population entered the Brahmaputra River system from Bay of Bengal. Various studies have shown the Hilsa population differs significantly from one another found in different rivers. In the present communication attempt has been made to investigate population of Hilsa shad in the Brahmaputra River using cytochrome b gene. Analysis of 425 bp of Cytochrome b gene fragment revealed 4 haplotypes with two clusters in dendogram. Existence of three polymorphic sites in the haplotypes sequences obtained from two groups of Hilsa shad showed low genetic differentiation in the Brahmaputra River. Keywords: Cytochrome b gene, Brahmaputra river, Tenualosa ilisha | 
