The tucuxi (Sotalia fluviatilis), alternatively in Peru bufeo gris or bufeo negro, is a species of freshwater dolphin found in the rivers of the Amazon Basin. The word tucuxi is derived from the Tupi language word tuchuchi-ana, and has now been adopted as the species' common name. Despite being found in geographic locations similar to those of 'true' river dolphins such as the boto, the tucuxi is not closely related to them genetically. Instead, it is classed in the oceanic dolphinfamily (Delphinidae).
Physically, the species resembles the bottlenose dolphin but differs sufficiently to be placed in a separate genus, Sotalia. The costero (Sotalia guianensis), related dolphins present in coastal and estuarine environments and formerly grouped together with the tucuxi, have recently been recognized as a distinct species.
