Present study is a first-time report of flathead Sillago, Sillaginopsis panijus (Hamilton, 1822), from Rupnarayan River of West Bengal. Seasonal sampling performed from January 2019- February 2020 by collection of water sample and fish sample in the morning time 5.00 A.M. – 8.00 A.M. A total of 116 specimens of Sillaginopsis panijus (Hamilton, 1822) were collected from four different sampling stations of Rupnarayan river (22.23°N 88.03°E to 22.40°N 87.36°E), West Bengal, India. Present work is a morphometric and meristic data analysis has been provided in detail. Total 23 morphometric characters and 13 meristic characters were analyzed. Morphological characteristics of the species were present to confirm the occurrence and distribution of Sillaginopsis panijus (Hamilton, 1822) along the riverine water of Rupnarayan. The physico-chemical parameters of water have been measured such as temperature of water, dissolved oxygen, pH and salinity. The statistical analysis of multivariate test with post-Hoc analysis and correlation were established with the abundance of S. panijus (Hamilton, 1822) in relation to water parameters. The result shows the dissolved oxygen, temperature, pH and salinity played a most important role in the distribution of S. panijus (Hamilton, 1822). The result shows a statistically significant difference in distribution of fish species, F (12, 8) =18.86, p<0.0005; Wilk’s Λ=0.001, partial η2=0.966. Present study certainly provides the baseline information of Sillaginopsis panijus (Hamilton, 1822) from the Rupnarayan river of West Bengal, India. This record of Sillaginopsis panijus (Hamilton, 1822) may assist the fishery scientist, researchers, policy planners and conservationists to develop sustainable fishery management. Therefore, this study was considered as a first step on morphometric characters for its development and documenting the extension of the distribution and ecological changes in its natural habitat which helps to conserve this species abundance in this area and prevent overexploitation.