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Not AvailableThe collected information on alien fish species revealed presence of 31 fish species introduced in the country for aquaculture purpose while over 600 varieties of ornamental aquarium fishes. Many of them were illegally introduced and their historical information was not available. In this paper, we have generated scientific information on the distribution of alien f ish species in different natural aquatic bodies and assessed their adverse ecological consequences such as decline of local fish species, competition with local species for food and feeding, space and spawning; threats to species integrity and ecosystem. A number of invasions of freshwater exotic fishes have taken place into India over the past decade and adversely affected the fish biodiversity. Many more changes are predictable to occur with the expected climate change invading newer areas and ecosystems. The estimated annual average production of alien species fit for human consumption amounts to around 18.2 to 34.5% of the annual average production of marketable fish cultures in India. A signif icant negative impact of the introduced species on native ichthyofauna has been ascertained as regards to its ecological, biological characteristics, biodiversity and health. Considered a typical invasive alien species, Oreochromis mossambicus, O. niloticus and Cyprinus carpio heavily depressed the occurrence and numbers of indigenous populations and also contributed to the declined f ishery of native cyprinid f ish species in several natural aquatic bodies of the country.Not Availabl