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Dikhow River is one of the largest tributaries of the Brahmaputra river basin originating from Yezami village near Zunheboto town of Nagaland. It debouches into the mighty river Brahmaputra river at Dikhowmukh, Sivasagar district, Asam covering a length of 255.8 km contributing 0.7% runoff. The geographical area of the Dikhow catchment is approximately 3100 km 2 , covering 85% of Nagaland, 10% of Assam and 5% of Arunachal Pradesh. The study area of the entire river stretch was divided into 6 stations whose elevation ranged from 90.83 msl to 669.9 msl (3 in Nagaland and 3 in Assam). These stations were selected to study the hydro-biological profile of the river stretch, its pollution status and fish diversity from January 2019 to February 2020. The important physico-chemical water quality parameters of the river in these stations like Dissolved Oxygen (5.2-10.1 mg/L), pH (7.0-8.2), Turbidity (3.8-143.8 NTU), Total Hardness (24.02-121.01 mg/L), Total alkalinity (33-89 mg/L), etc. were found to be ambient for the survival of aquatic fauna in some parts in some period of the year.

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Background: River water and its faunal diversity are regarded as an integral part of the environmental stability and river ecosystem. To know the abundance and diversity of fin fishes in relation to their environmental parameters, a hilly river Umtrew in Meghalaya and Assam was investigated during January, 2019 to December, 2020. Methods: Fish, plankton and water samples were collected regularly at monthly intervals for a period of 24 months. Standard protocols were followed for analysis of the collected samples. Result: A total of 49 fish species under 36 genera, 20 families and 10 orders were recorded. Among them Cypriniformes (42%) is the dominated order followed by Siluriformes (24%). As per IUCN status 1 species falls under critically endangered, 4 species are near threatened, 2 species under vulnerable and 42 species are of least concern. A significant correlation between species distribution and environmental variables was also reported. Our findings clearly oppose the tendency for species composition to increase from the source to the mouth of the river, which is probably prohibited by two major anthropogenic activities. These activities could constitute in the future a real threat for the fish population and other aquatic organisms.