Fish Community Structure and Environmental Drivers in a Tropical River Wetland Continuum: A Study From Brahmaputra Basin in the Eastern Himalayan Region

Abstract

The study investigates the fish community structure and environmental drivers of Deepor Beel, a floodplain wetland situated in the Brahmaputra Valley of Assam, India. Recognized as a Ramsar site of international importance, Deepor Beel is a biodiverse habitat that supports a variety of flora and fauna, including a rich ichthyofaunal diversity. This research recorded 55 fish species across 9 orders and 21 families, with Cypriniformes and Cyprinidae being the dominant order and family, respectively. Seasonal variations were evident, with the monsoon season exhibiting the highest species richness due to the beel's connectivity with the Brahmaputra River. Environmental factors such as water temperature, pH, dissolved oxygen, turbidity and ammonia levels were identified as critical determinants of fish abundance and community structure. The study applied biodiversity indices like Shannon–Wiener, Margalef and Simpson indices to quantify species richness and evenness, highlighting significant diversity fluctuations across seasons. The monsoon and postmonsoon period recorded higher diversity and species richness compared to the winter and premonsoon period. The research also highlights the growing threats to Deepor Beel, including eutrophication, habitat degradation, pollution and the introduction of non-native species. Despite these challenges, the beel remains an important ecological and economic resource, supporting fisheries and local livelihood. The findings underline the necessity for a sustainable management approach, including the implementation of conservation strategies to mitigate anthropogenic disturbances and preserve the ecological integrity of Deepor Beel. The study offers baseline data crucial for guiding future conservation efforts and emphasizes the need for formal management plans to ensure the long-term sustainability of this vital wetland ecosystem.