List of freshwater fauna of Sri Lanka explained

Sri Lanka is an island close to the southern end of India with a tropical environment. The freshwater fauna is as large as it is common to other regions of the world. There are about two million species of arthropods found in the world, and still it is counting with many new species still being discovered. It is very complicated and difficult to summarize the exact number of species found within a certain region.

Freshwater habitats

Freshwater animals are important to the economy of a country. The animal life in freshwater comprises a great diversity. The organisms ranging from tiny protozoa to large mammals in size. Sri Lanka is a hydraulic civilization. First civilizations in Sri Lanka were originated closer to main rivers in Sri Lanka such as Mahaweli, Kelani, Malwathu and Gin Ganga. Rivers in Sri Lanka flow in a radial pattern, from central hills where there are numerous waterfalls, the rivers flowing to the west, east and south being shorter than thoe flowing to north., north west and north east. Several streams join these rivers. Some of the streams in the hill country and mid country are quick flowing streams known as torrential streams.

Sri Lankan freshwater habitats can be divided into 6 major types - river, stream, lake, pond, villu and paddy field - according to size, depth, rate of flow and type of bottom. Medium-sized rivers are called Oya and fast flowing streams torrential streams are called Dola in Sinhalese. The following list provide the freshwater fauna of Sri Lanka.

Adaptations of freshwater fauna

The life history of any animal is divisible into 3 phases, initially a period of slow development, followed by a rapid growth with a voracious appetite and finally to an adult which breeds at regular intervals and continue to grow slowly. Most freshwater animals breed during or after monsoon rains where water is available for the young to spread over a wide area where crowding is less and there is a plentiful supply of food in the form of minute plants and animals.[1]

During dry season, conditions in temporary habitats become less and less favourable for aquatic animals. Those cut off in small habitats are quickly killed off, others in larger habitats survive longer. During this period, food become scarce and water level reduces. Animals become weakened or diseased and die or are eaten by birds and terrestrial animals. Many freshwater animals show adaptations to drought conditions. Fish with air breathing ability, utilize atmospheric oxygen to moisten gills, mud burrowing ability are some of them. Smaller crustaceans, produce eggs with hard resistant covering capable of surviving even a severe drought. These cysts are blown by wind and the species is dispersed. Freshwater crabs and prawns carry their eggs until they hatch out, while leeches carry the young in a pouch.

Researches on Sri Lankan freshwater fauna

Knowledge of Sri Lankan freshwater fauna has been considerably enhanced in the last twenty years or so in two ways. One is through the publication of monographs. The other way is through Swedish Expedition and Smithsonian Institution.[2] Several animals groups were identified extensively from Sri Lanka, such as fish, amphibians, odonates and arthropods.[3] Other freshwater fauna of Sri Lanka need more detailed work, which are currently based on the notes of way back in British period.[4] According to the National Red Data List in 2012, many freshwater habitats are degraded at an alarming rate due to rapid human interference. Habitat destruction, fragmentation and loss of forest cover has increased in past decade rapidly. The result becomes severe, where many amphibians have been not recorded after their discovery, which led the scientists to categorize Sri Lanka as a biodiversity hotspot.[5]

Protozoa

Family: Amoebidae

Family: Actinophryidae

Phylum: Ochrophyta
Order: Actinochrysophyceae

Family: Arcellidae

Family: Centropyxidae

Family: Ceratiaceae

Family: Clathrulinidae

Phylum: Cercozoa
Class: Granofilosea
Order: Desmothoracida

Family: Codonellidae

Family: Difflugiidae

Family: Epistylidae

Family: Euglenaceae

Family: Euglyphidae

Phylum: Cercozoa
Class: Imbricatea
Order: Euglyphida

Family: Glaucomidae

Family: Hyalospheniidae

Family: Ichthyophthiriidae

Family: Oxytrichidae

Family: Parameciidae

Family: Pelomyxidae

Family: Peridiniaceae

Family: Trichodinidae

Family: Volvocaceae

Family: Vorticellidae

Moss animals

Phylum: Bryozoa
Class: Phylactolaemata
Order: Plumatellida

Family: Pectinatellidae

Family: Plumatellidae

Hairybacks

Phylum: Gastrotricha
Order: Chaetonotida

Family: Chaetonotidae

Sponges

Phylum: Porifera
Class: Demospongiae
Order: Spongillida

Family: Spongillidae

Cnidarians

Phylum: Cnidaria
Class: Hydrozoa
Order: Anthoathecata

Family: Hydridae

Wheel animals

Sri Lankan freshwaters are home for 124 species of wheel animals.[6]

Flatworms

Phylum: Xenacoelomorpha
Order: Acoela

Family: Convolutidae

Phylum: Platyhelminthes
Order: Rhabdocoela

Family: Scutariellidae

Family: Typhloplanidae

Phylum: Platyhelminthes
Class: Trematoda
Order: Plagiorchiida

Family: Pleurogenidae

Phylum: Platyhelminthes
Class: Cestoda
Order: Bothriocephalidea

Family: Bothriocephalidae

Roundworms

Phylum: Nematoda
Class: Enoplea
Order: Dorylaimida

Family: Dorylaimidae

Class: Chromadorea
Order: Rhabditida

Family: Camallanidae

Gordian worms

Phylum: Nematomorpha
Class: Gordioida
Order: Chordodea

Family: Chordodidae

Segmented worms

Phylum: Annelida

Family: Aeolosomatidae

Class: Clitellata
Order: Haplotaxida

Family: Naididae

Family: Almidae

Order: Rhynchobdellida

Family: Ozobranchidae

Family: Galeommatidae

Family: Glossiphoniidae

Order: Arhynchobdellida

Family: Hirudinidae

Molluscs

Phylum: Mollusca
Class: Gastropoda
Order: Cycloneritida

Family: Neritidae

Order: Caenogastropoda

Family: Pachychilidae

Family: Thiaridae

Notes and References

  1. Web site: Some aspects of ecology of endemic freshwater fishes of Sri Lanka . University of Kelaniya . 12 April 2019.
  2. Web site: Guide to the Freshwater Fauna of Ceylon (Sri Lanka) . Bull. Fish. Res. Stn., Sri Lanka (Ceylon), Vol. 25, Nos. 1 and 2, 1974 pp. 27-81 . 12 April 2019.
  3. Web site: Sri Lanka Freshwater Fauna and Fisheries. A Guide to the Freshwater Fauna of Sri Lanka and a Genesis of the Fisheries by CH Fernando and SR Weerewardhena (2002) . African Journal of Aquatic Science . 12 April 2019.
  4. Web site: A guide to the freshwater fauna of Ceylon . Bulletin of the Fisheries Research Station, Ceylon . 12 April 2019.
  5. Web site: The National Red List 2012 of Sri Lanka . Biodiversity Secretariat of the Ministry of Environment . 12 April 2019.
  6. Web site: Rotifera froin Sri Lanka (Ceylon) new Species with a List of Rotifera Recorded and their Distribution in Different habitats from Sri Lanka . Bull. Fish. Res. Stn., Sri Lanka (Ceylon), Vol. 25, Nos. 1 and 2, 1974, pp. 83-96 . 12 April 2019.