Guwahati: In a discovery that reshapes understanding of fish migration in the Brahmaputra basin, a species traditionally associated with coastal and estuarine waters has been recorded for the first time in Arunachal Pradesh.
The Congaturi halfbeak (Hyporhamphus limbatus), a slender, beak-jawed fish commonly found along India’s western coast and in brackish waters, has now been documented from the Siang river at Pasighat, marking its first-ever record from Arunachal Pradesh and the upper Brahmaputra drainage.
The discovery adds a new dimension to the ecological importance of the Siang—one of the least studied major rivers in India, despite being the primary Himalayan artery feeding the Brahmaputra.
The halfbeak fish specimen was collected from the river Siang near the confluence point of Sibo Korong (stream) and the Siang river at Pasighat using a cast net. Photographs and maps in the study show the exact collection site and the fish’s distinctive elongated body and protruding lower jaw—features that give halfbeaks their name.
The finding has been published in the Asian Journal of Fisheries and Aquatic Research by zoologist Kento Kadu of Jawaharlal Nehru College, Pasighat.
Originally described from the Malabar Coast in the 19th century, Hyporhamphus limbatus is known to be euryhaline—capable of tolerating both salt and freshwater. While it has previously been reported from rivers such as the Ganga, Hooghly, Mekong and even Himalayan rivers in Nepal and Bangladesh, it had never been recorded from Northeast India.
The Siang River, which enters India from Tibet before becoming the Brahmaputra in Assam, lies hundreds of kilometres upstream from the coast. The presence of a coastal-associated fish species here suggests remarkable upstream migration and highlights how little is still known about fish movement in Himalayan river systems.
“The present study provides the first record of Hyporhamphus limbatus from the Siang river of Arunachal Pradesh andthe distribution range of the species upto upper reaches of the Brahmaputra drainage. The finding is a new addition to the fish species list of the state, as well as the North-Eastern region of India. However, the reasons for their broad upstream migration, especially in the Brahmaputra basin, are not known and further study in this direction is necessary. An in-depth study on habitat preferences, ecological dynamics, and migratory behaviour of Hyporhamphus migratory limbatus is necessary, considering the ongoing climate changes,” Kadu says.
Arunachal Pradesh is part of the Eastern Himalayan biodiversity hotspot, yet many of its rivers remain poorly explored in terms of fish diversity, particularly in fast-flowing, high-altitude systems like the Siang. Despite extensive ichthyological surveys over decades, Hyporhamphus limbatus had never been listed from the state.