Post-impoundment changes in fish diversity and community structure of the Dikrong River, Arunachal Pradesh: a comparative assessment between 2000–2001 and 2025–2026

Abstract

A study carried out on the dam impacted Dikrong River, which is one of the major tributaries of the Brahmaputra in Arunachal Pradesh, suggests that the river has undergone significant ecological alteration following the commissioning of the Sopo dam in 2018 and increasing anthropogenic pressures. The present study attempted to assess the fish diversity, community structure, trophic composition, and conservation status in the Dikrong River during 2025–2026 and the results were compared with pre-impoundment records made in the year 2000–2001. A total of 27 fish species belonging to 24 genera, eight families, and three orders were recorded, with Cyprinidae dominating the assemblage (51.9%). Opsarius bendelisis was the most abundant species (44.1%). The taxonomic comparison with previous data reveals an apparent reduction in the number of species, mainly bottom feeders, which highlights their sensitivity to flow regulation and habitat modification. There was a change in the food chain from the dominance of bottom feeders to column feeders. Water release from regulation, riverbed quarrying, and runoff reduced the quality of the habitat and fish behavior. The juveniles of Semiplotus semiplotus, Opsarius bendelisis, and Devario aequipinnatus were found to be accumulating in the clean-connected drainage system downstream (polluted zone). The findings suggest a need for environmental flow regulation and habitat restoration to conserve remaining fish diversity. Further, the study recommends promotion of culture-based fisheries selecting some of the indigenous ornamental and food fish as a future conservation and livelihood strategy.