Ichthyodiversity of the River Lakhandei at Runni Saidpur, Sitamarhi (Bihar)

The River Lakhandei is a significant tributary of the Bagmati river under the Ganga River system. It serves as a vital life-line for the district of Sitamarhi, particularly in the Runni Saidpur block. This article provides an exhaustive analysis of the ichthyodiversity (fish diversity) of the river at Runni Saidpur, examining species composition. Based on field observations we collected and identified 47 fish species from the Lakhandei River at Runni Saidpur, Sitamarhi, Bihar. The collected 47 species belong to 36 genera under 19 families and 9 orders. The most abundant order in terms of species diversity was Cypriniformes, an usual event in the rivers of the Gangetic plain. The order has 23 species under 17 genera and 4 families. Percentagewise it stands respectively as 48.94%, 47.22% and 21.05%. Its one family, Cyprinidae containing 12 species under 7 genera, is the most diverse fish family of the area. Its another family Danionidae, with 8 species under 8 genera, stands second. The second largest order is Siluriformes with 10 species under 8 genera and 6 families. It is the most diverse local fish order in terms of family diversity. The results are similar to that reported from Baya River, a tributary of the Ganga. Percentagewise, its species, genus and family share stands respectively as 21.28%, 22.22%, and 31.58%. Its largest family Bagridae having 3 species under single genus Mystus, is the third most diverse family, jointly with Mastacembelidae (order Synbranchiformes ≈ Mastacembeliformes) having 3 species under 2 genera. Anabantiformes stands at 3rd position with 3 families while all other orders namely Osteoglossiformes, Clupeiformes, Beloniformes, Gobiiformes, Synbranchiformes and Tetraodontiformes contain one family each. Most of the reported species are categorized in IUCN Red List (2024-25) as Least Concern (LC) but several key species are under threat. Chitala chitala (Notopterus chitala), Labeo pangusia, Ompok pabda, and Ailia coila are Near Threatened (NT) while Wallago attu and Cyprinus carpio is Vulnerable (VU). Two species, Cyprinus carpio and Ctenopharyngodon idella are introduced (exotic) species while rest were native one. Cyprinus carpio is also an Invasive Species. However, increasing anthropogenic pressures such as pollution, embankment construction, unregulated fishing, and seasonal water scarcity pose significant threats to its fish diversity, highlighting the urgent need for conservation.