Ecology and ichthyofaunal diversity of Dirang Chu: a key Himalayan snow fed river of Arunachal Pradesh, India

Arunachal Pradesh, a Himalayan state of India, is divided into five river valleys; the Kameng, the Subansiri, the Siang, the Lohit and the Tirap. All these are fed by snow from the Himalayas and countless rivers and rivulets. The Dirang river valley resembles typical V-shaped valley of Himalayan terrain surrounded by denudation hills. The study embodies to carry out ecological and biological characteristics of the river Dirang, which harbor several important coldwater fish species like snow trout, loaches etc. in order to develop a suitable management plan for sustainable utilization of these Himalayan mountain resources. Physicochemical parameters of water such as dissolve oxygen content and temperature of Dirang river was found to be optimum for the habitat of coldwater fishes. The river water has relatively alkaline pH values ranging from 7.2 to 7.6. Phytoplankton density ranged from 3–40 individuals/l at various sampling sites, which was dominated by the members of Bacillariophyceae. Zooplankton density ranged from 3–27 individuals/l and Periphyton 60–120 individuals/cm2. The river supports diverse fish species of which many are endemic to the region. Fish species like the Schizothorax sp, Botia sp, Barilius bendelisis, B. bola, Punitus spp, Torputitora, Danio spp., Garra spp., Gotyla gotyla, Anguilla are found in the river drainage. Several spawning grounds of the coldwater species are also identified in the river valley which needs protection for conservation.