Plankton minute organisms known to occur in every aquatic habitat which have either relatively small power of locomotion or none at all, and drift or float passively with current or the waves. All aquatic habitats are populated with littoral, planktonic and benthic communities consisting of plants and animals. Planktonic communities are usually represented by major groups of algae and invertebrate organisms, like green algae, blue-green algae, desmids, diatoms, protozoans, rotifers, cladocerans, copepods, and ostracods. Moreover, some immature stages of fishes, various animal larvae and worms are also found in plankton communities as occasional plankter.

The planktonic community occupies an important position in the aquatic world for their indispensable role in the ecosystem; small or microscopic in size, their absence might lead the entire life processes to a halt. The plant originated planktons (phytoplanktons) play the vital role in synthesizing the light energy into food, while some animal originated planktons (zooplanktons) acting as primary consumers of phytoplankton and thus transferring the energy from producer to next tropic level, initiate the transfer of energy from one living organism to another. Some fishes remain plankton feeders throughout their life and most of the carps are mainly plankton feeders. It is universally accepted that the richest fisheries of the world are closely related to plankton production in aquatic habitat.

The aquatic habitat of Bangladesh is rich in both phytoplankton and zooplankton. Although a complete systematic list on the phyto- and zooplanktonic organisms of Bangladesh is not available, the major known genera of phytoplankton are Eudorino, Pleodorina, Volvox, Chlorococcum, Pediastrum, Oocystis, Tetrallantos, Sceredesmus, Coelastrum, Ulothrix, Gloeotila, Oedogonium, Cladophora, Lola, Stigeoclorium, Mougeotia, Zygenma, Spirogyra, Microcystis, Aphanothece, Syechococcus, Merismopedia, Dactylococcopsis, Spirulina, Oscillatoria, Lynabya, Schizothrix, Symploca, Microcoleus, Wollea, Nostoc, Aradaera, Raphidiopsis, Scytorema, and Gloeotrichia.

The major genera of zooplanktonic organisms are Diaptomus, Heliodiaptomus, Neodiaptomus, Cyclops, Mesocyclops, Macrocyclops, Microcyclops, Cypris, Stenocypris, Cyclestheria, Pleuretra, Rotaria, Embata, Anuraeossia, Brachionus, Platyias, Keratella, Euchlanis, Dipleuchlanis, Triplechilanis, Macrochaetus, Mytilina, Epiphane, Diplois, and Monostyla. [Abdul Maleque Bhouyain]

See also phytoplankton.