Ganges river dolphins are usually a grey or light brown colour, but may also have a pinkish tone to the belly1. The dorsal fin is very small, and is a low fleshy lump on the back, usually just a few centimetres in height. The dolphins have a steep forehead, and flexible necks with unfused vertebrae which permit them to turn their heads from side to side. They have an elongated snout that can bend slightly upward; it can reach up to 20% of total body length in females. They have long, sharp teeth which are visible even when the mouth is closed. The pectoral flippers on the side of the body are large and paddle shaped.
This species is functionally blind, and therefore relies heavily on echolocation to navigate and hunt4, 16. Externally, the eye appears to be barely larger than a pinhole and therefore restricting light from reaching the retina, there is no lens, and the optic nerve is very narrow, leading scientists to conclude that their eyes are incapable of forming clear images, but that they may still serve as light receptors4, 16.
Ganges River Dolphin Illustration by Uko Gorter
Reproduction and growth
Not much is known about the mating and reproduction of Ganges river dolphins except that they breed year-round and most births are thought to occur between October-March17. Gestation is thought to be 8 to 9 months4, 18. At birth, calves are about 70 cm long, but adults can reach about 2.60m and weigh up to 90 kg as adults. Females are generally longer than males due to a longer rostrum1, 18.
Ganges river dolphin females give birth to a single offspring, usually weaning them within a few months. Males and females typically reach sexual maturity at approximately 10 years of age18. The oldest known Ganges river dolphin was a 30 year old male1.
Ganges river dolphins eat a large variety of small and medium sized fish and crustaceans19. It is thought they use echolocation clicks to scan and detect prey at distances of about 20 m but that they may use electroreception to detect prey that occurs near to the river bottom20.
Like Indus river dolphins, Ganges river dolphins have developed a unique side swimming behaviour which is an adaptation to help them navigate through shallow waters16. Dives are typically short, lasting between 70-100 seconds. Like other dolphin species, they navigate using echolocation, but reflecting the complexity of the river environment Ganges river dolphins emit sound almost constantly. Ganges river dolphins are most frequently found alone, but they also gather in small groups, sometimes with more than 10 individuals, at the confluence of tributaries19. Generally, these animals are shy towards humans.