Assessing Fish Population Diversity in Rangazak and Challou River of Manipur, India

Abstract

Two ecologically significant ecologically poorly known hill-stream systems within the Indo-Myanmar Biodiversity Hotspot in the Chindwin-Irrawaddy basin on the Chindwin coast of the Indo-Myanmar frontier, which feed the Indo-Myanmar coast, are the Rangazak and Challou rivers, in the northern part of Ukhrul District, Manipur, India. The first systematic evaluation of fish diversity in these rivers is reported in the study and aimed at to provide a baseline information on biodiversity tracking, conservation and sustainable management of the local aquatic resources. Three sites were sampled each in the rivers (dry season (February-April 2025) and monsoon season (May-July 2025)) with a common effort of cast nets, gill nets, scoop nets, angling and hand collection. Community evenness was estimated on the basis of the Shannon-Wiener diversity, Pielou evenness and Margalef richness indices. The total number of fish species was 24 representing 18 genera and 7 families (Cyprinidae was the highest species rich family). The composition of the community changed between seasons with the cyprinids (62.9% in Rangazak; 50.9% in Challou) being the prevailing group in the dry season and the rheophilic loach Schistura (Nemacheilidae) dominating in Rangazak in monsoons (52.5%). The indices showed moderate diversity (H 0-1.82-1.99), moderate evenness (J0-0.60-0.64) and high species richness (D-3.10-3.43) that were promoted by monsoon flooding and fish movement, breeding migration and assemblage renewal. The presence of several species that are sensitive to the environment like Glyptothorax, Pseudecheneis, Schizothorax and Tor are indicative of the fact that the rivers are highly environmentally intact but there is the scarcity of economically significant species (Tor, Neolissochilus, Semiplotus) and increasing human pressures on the system through destructive fishing and disturbance of habitats that make the rivers particularly significant as far as conservation is concerned.