There is no life without water. Water covers about 71% of the earth’s surface and provides the most extensive medium for aquatic animals to live. Man has utilized lakes, ponds and reservoirs as important water resources and exploited them for various purposes. Minute organisms called plankton occur in the waters bodies. Zooplankton are animal plankton. Plankton abundance and distribution are strongly dependant on factors such as ambient nutrient concentration, physical state of the water column and the abundance of other plankton. Zooplankton forms the basic link of food chain for all aquatic animals and fish yield to a great extent. The need for water is increasing day by day invariably due to increase in population, industrialization, urbanization etc. Simultaneously, the quality of standing water is deteriorating and is unfit to mankind due to human activities, neglect and mismanagement. To evaluate the quality of water with special reference to the Zooplankton some concepts are followed. Study of fauna, flora and biological indicators with biodiversity of the tank; Identification of the major pollution problems of water Tank. The zooplanktons like cladocerans ( for example: Diphonosoma exisom, Ceriodaphnia cornuta, Macrothrix goeldi, Monia Macrocopa, Alona Pulchela, Pleeuroxus trigonellus, etc.,), copepods (for example: Rhinediaptomus indicus, Heliodiaptomus, etc.),rotifers (for example: Brachionus Caudaus, Brachionus Plicatilis, Brachionus Calciflorus, Brachionus diversicornis, Brachionus Quadrifentatus, Brachionus falcatus, Brachionus bidentata, Brachionus ureolaris, etc.,) and ostracods are studied. The Parappana tank was investigated for monthly variation of zooplankton composition, and 44 species of zooplankton were recorded in these water reservoirs. Cladocera was taxonomically dominant group and copepoda was high in density. Reservoir was in eutrophic or hypereutrophic state in March to May (summer) and in winter seasons, in the remaining months it was either in oligotrophy or in mesotrophy state. Parapanna Tank has 44 species of zooplanktons Rotifera was taxonomically dominant group. Both Rotifera and Copepoda were equally dominant in density the pond.
