The Tucuxi (Sotalia fluviatilis), alternately Boto-cinza, Boto-cinza-marinho, is a 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.

The Tucuxi is coloured light to bluish grey on its back and sides. The ventral region is much lighter, often pinkish. The dorsal fluke is typically slightly hooked. The Tucuxi exist in small groups of about 10-15 individuals and swim in tight-knit groups, suggesting a highly developed social structure.