Indian Hydrobiology, 20(2): 263–268, 2021 Assessment of Ichthyofauna and Hydrological variables in Veluthodu, a Head water Stream of Pamba river in Kerala Ruby Thomas 1, * and K. Raju Thomas 2 1 Research Scholar, Department of Zoology, Mar Thoma College, Tiruvalla-689 103, Kerala, India 2 Assistant Professor in Zoology, Mar Thoma College, Tiruvalla-689 103, Kerala, India *Corresponding Author – rubythomas92@gmail.com Abstract Documentation of ichthyofaunal diversity and hydrological variables from Veluthodu, a headwater stream of Pamba river in Southern Kerala was carried out from January to December 2019. Dissolved oxygen (DO), total hardness, conductivity, Chemical Oxygen Demand (COD), and Biological Oxygen Demand (BOD) were estimated. A total of 18 species of fshes belonging to 13 genera, four families, and three orders were recorded. Of these, 14 are endemic and two are threatened. The family Cyprinidae formed the most abundant group with 10 genera, followed by Nemacheilidae, Bagridae, and Belonidae with one genus each. The order Cypriniformes formed the most dominating ichthyofaunal order (89%) in the investigated stream. The pristine stream possesses moderate levels of total dissolved solids (TDS), hardness, and electrical conductivity. But pH and dissolved oxygen (DO) showed deviation from the accepted limits of BIS. Key words: Ichthyofaunal diversity; Veluthodu; Hydrological parameters; Endemism; Threat status. Introduction God’s own country, Kerala is home to a myriad of ecosystems and wildlife. The rivers of Kerala are originating from the global biodiversity hotspot- The Western Ghats. These river systems are the lifeline that supports pristine forests, endemic fora and fauna, and the great human civilization from time immemorial. Physical characteristic gradients such as gradients of depth, light penetration, and substrate characteristics always exist across river channels. These physical differences result in a range of niche formation for a variety of aquatic community (Townsend, 1989). Water chemistry is an important feature of an aquatic environment that regulates the growth and survival of its inhabitants. The fsh community is highly valued for its economic, social, nutritive, and aesthetic importance. The native fshes respond immediately to any kind of habitat destruction, changes in water chemistry, and the introduction of exotic fshes. So fshes are effective biological integrity indicators of an aquatic environment. Knowledge regarding ichthyofaunal resources of an aquatic environment helps to develop proper management and conservation strategies. A large number of fsh diversity studies were carried out in the streams and rivers of the Western Ghats (Ponniah and Gopalakrishnan, 2000; Renjithkumar et al., 2011; Lal et al., 2014; Athira and Jaya, 2020). The discovery of new species and rearrangement of taxonomic groups always added to the fshery resources of the country. Pristolepis rubripinnis is a new species of percomorph fsh described from the Pamba and Chalakudy rivers in Kerala (Britz et al., 2012). Plamoottil and Zupancic (2017) reported a cyprinid fsh Labeo fliferus from Pamba river. The present investigation was carried out to explore the diversity of ichthyofauna along with the hydrological parameters from the tributary of Pamba river in southern Kerala.