The iris is brown with a longitudinal oval pupil. In general, the tucuxi is dark gray on its dorsal side and pale pink on its ventral side with a distinct line separating these two regions. An area of pale gray starts behind the pectoral fin and another gray area starts from the mid-body and runs to the anus. In the marine S. f. guianensis , the upper colorings range from pale bluish gray to brown or black. The color of the back extends to a circle around the eye, onto the pectoral fin, and to the sides of the tail.
Some populations have yellow-orange sides with a bright patch on the sides of the dorsal fin.
In S. f. fluviatilis , the upper parts are bluish or pearl gray. Furthermore, the tip of the beak and tip of the dorsal fin are occassionally white. S. fluviatilis is often confused with a smaller version of bottlenose dolphin. Sotalia has 26-35 teeth on each side of the jaw. The diet contains mostly fish and shrimp.