: Food chain is defined as a group of organisms in which there is a transfer of food energy through a series or repeated eating and being eaten. In pond ecosystem, phytoplanktons like Ulothrix, Spirogyra, Oedogonium, Chlamydomonas, Volvox, Pandorina, Anabaena etc. are the producers. Zooplanktons such as Dileptus, Coleps, Euglena etc. are the primary consumers (herbivores). Small fishes are secondary consumers while the big fishes are tertiary consumers.