South Asia, also known as Southern Asia, is the sub-region lying on the Indian Plate and bordered on the north by the Eurasian Plate. Geopolitically, the region is the Indian subcontinent, including the countries of India, Pakistan, Sri Lanka, Bangladesh, Nepal, Bhutan and parts of Afghanistan and Myanmar. It contains more than 20 freshwater ecoregions and two freshwater biodiversity hotspots, the Eastern Himalaya and the Western Ghats-Sri Lanka. South Asia region also encompasses parts of the Sundaland and Indo-Burma hotspots.
The region is known for its varied geographical features ranging from glaciers to rainforests and deserts to grasslands and mangrove forests. This diversity in habitats and climatic conditions has resulted in the occurrence of high levels of diversity and endemism of flora, fauna and fungi.
The freshwater ecosystems of South Asia harbour exceptionally high ichthyofaunal diversity and endemism. The total number of freshwater fishes in the South Asia could probably exceed 1000 species, under about 300 genera and 70 families. India harbours the greatest number of endemic freshwater fish species in continental Asia. Afghanistan has more than 100 species, which is a mixture of native, central Asian, introduced and invasive. Although fish fauna of the major rivers have been identified and documented, many of the interior areas have not been fully explored. The species is still in the discovery survey state and more and more new taxa continue to be described. Several taxonomic problems, evolutionary conundrums and biogeographic hypothesis remain to be solved.
Freshwater fish fauna of South Asia face several threats to their continued survival. Recent assessments of the state of freshwater fish diversity in two of the most important biogeographic regions in South Asia, i.e. Western Ghats and Eastern Himalaya, revealed that 33% and 14% (respectively) of fish species are threatened. One in every two freshwater fishes in Sri Lanka are also known to face a threat of extinction. Major threats to the freshwater biodiversity of the South Asia region include pollution, habitat loss, overfishing, flow modification and alien invasive species.
Many universities, research organizations and Non-Governmental Organizations (NGOs) in the South Asia region are conducting awareness programmes, educational and outreach activities for freshwater biodiversity conservation. Central and State governments in India are also involved in restocking and enhancement activities in reservoirs and rivers. In the Eastern Himalaya, some of the "regionally extinct" in the wild species, namely Osteobrama belangeri and Bangana devdevi, have been successfully bred in collaboration with expert fish farmers and are now cultured in farms. IUCN Red Listing of freshwater fishes of many regions including Western Ghats, Eastern Himalaya, Sri Lanka and Pakistan have been carried out in collaboration with IUCN and several other local, national and international partners. Projects that are based on "Key Biodiversity Areas" and "Alliance for Zero Extinction" sites are also being implemented in the region.
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Rajeev is interested in interdisciplinary research, advocacy and policy making related to the conservation, management and sustainable use of freshwater biodiversity. Much of his work is carried out in the Western Ghats region of South India, part of a global biodiversity hotspot (Western Ghats-Sri Lanka).
Rajeev is also associated with the IUCN SSC in several capacities, including as the freshwater representative on the IUCN SSC Red List Committee, and a member of the FFSG steering committee.
Professor Vishwanath is engaged in teaching fish and fisheries, and inventory and characterization of freshwater fishes of eastern Himalaya. He delivers lectures related to freshwater fish conservation in meetings with the village authorities and students bodies, and also at the regional and national seminars. He is also engaged in research planning for inventory of fish genetic resources and conservation. Professor Vishwanath is now the Chairman of Research Advisory Committee of National Bureau of Fish Genetic Resources, Lucknow, India and a member of the Manipur State Expert Appraisal Committee for environment, constituted by the Ministry of Environment and Forests, Government of India.