We will talk about 3 fresh water dolphins that are native to the Ganges, Indus and Irrawaddy rivers. They have adopted themselves to live in these rivers and scoop the food from the bottom of the shallow rivers.
First one is the Gangetic Dolphin, known scientifically as Platanista Gangetica Gangetica. As the name suggests it is found in river Ganga down to Sundarbans delta. But they are also found in Brahmaputra river. Locally they called Susu and has been declared national aquatic animal of India. The females are larger than the males and the size of these dolphins varies between 2.3 to 2.6 meters. The dorsal fin is like a ridge and very insignificant. These dolphins lack eyesight which will be of course of no use in the muddy waters of these rivers. That is why they are sometimes called blind dolphins.
They locate the shrimps and fish by echolocation. They are said to swim in tilted manner. This may be due to the fact that they may be using this technique to sense the bottom and locate themselves in the absence of eyesight which would have helped them to see the Snell’s window and orient themselves.
Second type of dolphins in this category are the cousins of Gangetic dolphins. They are called Indus dolphins and scientifically known as Platanista Gangetica minor. They differ from their cousins in the length of their tails which are smaller in size. They have long beak and poor eyesight. In fact they are subspecies of the Gangetic dolphins. They are found in the Indus river in Pakistan.
Third and last variety is found in Irrawaddy river of Myanmar. Known as Orcaella Brevirostris scientifically they are found in discontinuous water bodies in Bay of Bengal coast and estuaries. These have a rounded head with almost no beak. They are the relatives of Orca and due to very short beak are called Brevirostris. In the Irrawady river, they are said to herd the fish catch towards the fishing boats. In return the fishermen share some of the catch with them. They use very powerful jets of water to stun the fish. Sometimes they have been found to playing with stunned fish and discarded them after wards.
They are known by many names like Labai in Burmese and Khem and Khera in Oriya. In fact they it was given its name Irrawaddy dolphin by Sir Richard Owen in 1866 based on a specimen found in 1852, in the harbour of Vizag on the east coast of India.