Floodplain lakes form an integral component of major river systems of the world. In India, they are mainly distributed in Eastern Bihar, Uttar Pradesh, West Bengal and Northeastern India. Although limnological investigations in India began nearly one century ago, the review of the Indian literature indicates limited information on the structure and functioning of the floodplain lakes in spite of several routine hydro-biological surveys. Further, little is known till date about composition, distribution, abundance and ecology of the littoral and limnetic invertebrate communities and zooplankton biodiversity in these ecotones of India in particular.
The present comprehensive study on zooplankton diversity of the floodplain lakes ot Assam assumes special taxonomic and ecological importance in view of the stated lacunae. Plankton samples collected from 87 floodplain lakes of Assam are examined for analysis of the faunal diversity of zooplankton while investigations on their ecosystem diversity are based on regular seasonal collections from 30 lakes. Various documented taxa are briefly diagnosed and illustrated. Remarks are made on the general nature and composition of zooplankton fauna and their constituent groups, biogeographically interesting elements, indicator species, community similarities between different lakes and species diversity, dominance and evenness of dominant qualitative groups, namely Rotifera and Cladocera. In addition, comments are made on the influence of basic abiotic factors on richness and abundance of zooplankton and their dominant groups. The scope of the present observations is limited not only to typical euplanktonic taxa, which otherwise may be limited in the floodplain lakes, but also includes 'facultative zooplankton' and 'free-living micro-invertebrates' associated with various aquatic macrophytes frequently occurring in these wetlands.