Boto (Amazon River dolphin)

Inia geoffrensis
Other names: 
  • Amazon River dolphin
  • Pink river dolphin
  • Inia
Maximum length: 
  • Male: 2.5m
  • Female: 2.3m
  • Calf: 0.8m
Maximum weight: 
  • Male: 207 kg's
  • Female: Unknown
  • Calf: Unknown
  • Freshwater fish
  • Shellfish
  • Turtles
Estimated population: 
IUCN Listing: 
CITES Appendix: 
CMS Appendix: 

The boto, otherwise known as the Amazon River dolphin is endemic to South America and is the most studied of all the species of river dolphin. Currently the IUCN recognises three subspecies; I. g. geoffrensis in the Amazon River system of Brazil, Ecuador and Peru; I. g. humboldtiana in the Orinoco basin of Colombia and Venezuela; and I. g. boliviensis in Bolivia. However, recent genetic evidence has brought this classification into question. The Committee on Taxonomy (2012) list of marine mammal species and subspecies from the Society for Marine Mammalogy (SMM) has accepted the evidence for an additional species, Inia boliviensis, the Bolivian river dolphin, found solely in the river systems of Bolivia (and rivers along the Bolivia-Brazil border). Hopefully IUCN will make a similar announcement soon. The remaining two subspecies seemingly present no morphological differences and it is possible that they are in fact one species. 


The boto is a fairly robust animal with small but functioning eyes and a long slender beak that curves down slightly towards the tip. The boto and the Araguaian and Bolivian river dolphins are the only toothed whales to have different types of teeth in their jaw, those in the front are the usual simple conical shape whilst those in the back are designed to aid in the crushing of prey items. The melon is bulbous and abrupt, and the dolphin is able to change the shape of its melon. The crescent shaped blowhole is set left of centre and the neck is very flexible due to unfused cervical vertebrae, and has a well defined crease. The boto has a long dorsal ridge and very low dorsal fin. The flippers are triangular, broad and have blunt tips, while the flukes are triangular, broad and have pointed tips. Both flukes and flippers have ragged trailing edges. One of the most striking characteristics of the boto is its colouration, ranging from white/grey to pink on the dorsal surface, and a paler colour below. Some individuals however are a vivid pink colour. The colouration is highly variable and affected by age and viewing conditions. As the only other cetacean to share the boto's range is the tucuxi, it is almost impossible to confuse it with any other species.


Another feature of this primitive looking dolphin are the 'chubby cheeks' which it is believed may obstruct its downward vision and may be the reason they are often seen swimming upside down. Botos are typically slow swimmers, more active in the early morning and late afternoon, although when feeding they can show short bursts of speed. They are generally seen alone or in pairs, but during the dry season or in the presence of abundant prey they will congregate in groups of some 10 to 15 individuals. Botos are not an acrobatic species and rarely leap from the water. They also breathe at a rather shallow angle, showing beak, melon and dorsal fin all at the same time. Botos feed on fish, shellfish, and even small turtles.


The boto is found throughout the Orinoco and Amazon River basins, in the mainstems of the rivers, their tributaries and lakes, although in some localities its natural range has been restricted by development and the building of dams. During the wet season its range extends into the flooded forests. The major threat to this species is directed hunts where the animals are either used for bait or seen by fishermen as competition. Other threats to the species include human disturbance, entanglement in fishing gear, prey depletion, and chemical pollution. The IUCN Red List categorises this species as Data Deficient.

Distribution map: