By Dr. Lalthlamuana Pachuau
Research Associate
Mizoram Pollution Control Board
Studies on fresh water bodies such as ponds, lakes, reservoirs, wetlands, rivers, streams have gained much importance in recent years due to their importance. These water bodies harbours wide array of aquatic organisms, in particular Plankton. They form a very important part of fresh water community and contribute significantly to aquatic productivity. Therefore, the information about plankton is essential to understand the functioning and trophic dynamic of different water bodies. In addition certain planktonic organisms are valuable indicators of trophic status of various aquatic biotopes.
Plankton are microscopic organisms that live suspended in the water environment and thousands of these organisms can be found in fresh water ecosystem, many factors can affect the distribution of plankton in an ecosystem and can be divided into two categories – Phytoplankton and Zooplankton.
Among these two categories, Cladocera under Zooplankton is one of the most interesting group and are commonly termed as ‘water fleas’ because of their characteristics jerky swimming action of location. They are found in almost every type of fresh water biotopes and play a vital role in aquatic food chain and they serve as major prey items for many species of invertebrates and vertebrates. Further, Moina and
Daphnia species are cultured and used as supplementary live fish-food for various pisiculture and aquaculture practices.
General morphology: Cladocerans are microscopic organisms generally range in size < 250 μm in chydorid genus, 4 – 6 m in daphniid genera and leptodora genus is the largest member which can reach up to the length of 18mm. The cladocerans in general are characterized by the presence of their two biramus antennae which is used for locomotion. Head consist of large compound eye and ocellus is present in certain species. The carapace (hard upper cell of the body) is rounded, oval or elongated with or without posterior spine and generally have five or six pairs of thoracic limbs.
Collection and preservation and identification: Plankton samples can be collected by towing or dragging Nylobolt plankton net (no#25) in open-waters bodies and preserved in 5% formalin. The collected plankton samples are screened by taking out a few drops of samples with the help of a dropper and put on a slide and screened by using stereoscopic dissecting binocular microscope. Different taxa will be identified following important works of Michael and Sharma (1988), Smirnov (1971, 1976), Korovchinsky (1992) and other relevant literature.
Study sites in Mizoram: Plankton samples were collected from different water bodies in various districts of Mizoram such as Lake (3 places), Wetland (3 places), Fish Pond (10 places), Reservoir (2 places), Paddy field (4 places), Stream (2 places), Seepage water (1 place).
Result: 18 species of Cladocera are documented (photograph shown below); among these the most common species recorded is Chydorus sphaericus. This is just a preliminary survey in the state of Mizoram and it is expected that there are still many more species yet to be discovered in this field.
Written by Lalremruata
A man with hobby of reading, writting
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