Assessment of Ichthyofaunal Diversity and Habitat Variables in Himalayan Brahmaputra River of Assam, North-Eastern India

In the present communication, we report ichthyofaunal diversity and habitat variables from eight major landing centers spread across three stretches (upper, middle and central) of River Brahmaputra in Assam from 2019 to 2021. The environmental variables such as temperature (21.2–28.6 °C), dissolved oxygen (6.52–8.27 mg/l), pH (7.1–8.2), alkalinity (62–87 mg/l), nitrate (0.018–0.038 mg/l) and phosphate (0.003–0.016 mg/l) were observed to be in a suitable range for aquatic fauna and flora. From the studied region, 110 fish species belonging to 33 families and 69 genera were reported. Among the families, Cyprinidae was the most prevalent family representing 42.73% then Bagridae (6.38%), Channidae (6.36%), Ambassidae and Osphronemidae (3.63%), Badidae, Mastacembelidae, Schilbeidae Siluridae, and Sisoridae (2.73%), and other families contributing about 1%. According to the International Union for Conservation of Nature and Natural Resources (IUCN) status, two species were included under Endangered category, two species under Vulnerable category, 6 species under Near threatened, 4 species have Data deficient and 96 species under Least concern category. Most of the fish species observed were indigenous, with a few endemic and rare species in the region. Small indigenous fishes (such as Cabdio morar and Ailia coila) are the most abundant fish species. Fish species richness and diversity indices showed seasonal fluctuation. Highest species richness (105) was observed during pre-monsoon, then post-monsoon (88), and monsoon (82) seasons. The Shannon (H′) indices varied from 3.45 (monsoon) to 3.86 (pre-monsoon), with an evenness index between 0.38 (monsoon) to 0.45 (pre-monsoon) indicating a slightly impacted pattern of the studied river stretch i.e., (H′) > 3.0. Various natural and man-made threats are presumed to affect biodiversity in River Brahmaputra. Therefore, strategies such as fish harvest regulation, desiltation, controlling of water pollution and anthropogenic activities are suggested for conservation of the aquatic biodiversity in the River.